JPLCLOCK – Orologio multifunzionale (Software MS-DOS)

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INFORADIO

JPLCLOCK – Orologio multifunzionale (Software MS-DOS)

Disponibile alla seguente pagina: http://www.forumradioamatori.it/download/download-dos/HamSoft/HamSoft.html



                             Program JPLCLOCK

            NASA/JPL Multimission Computer Control Center Clock


               (C) Copyright David H. Ransom, Jr., 1991-1994
                           All rights reserved.


                               Version 9401
                             January 01, 1994


                          by David H. Ransom, Jr.
                          Rancho Palos Verdes, CA


                           CompuServe: 75240,176


                     RPV ASTRONOMY BBS  (310) 541-7299
                      RPV HOTLINE BBS  (310) 544-8977
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock         




                             TABLE OF CONTENTS
                             -----------------


INTRODUCTION ......................................................1
     JPLCLOCK FEATURES ............................................1
PROGRAM DESCRIPTION ...............................................5
JPLCLOCK HARDWARE AND SOFTWARE REQUIREMENTS .......................7
JPLCLOCK FILES ....................................................9
Programs TIMESET and RIGHTIME .....................................10
STARTING PROGRAM JPLCLOCK .........................................14
     JPLCLOCK Command Line Options ................................14
     Setting UTC Zone and Daylight Flags ..........................15
JPLCLOCK MAIN CLOCK DISPLAY .......................................18
JPLCLOCK MAIN MENU ................................................22
     F1   Program Information .....................................23
     F2   Set LOCATION CLOCKS .....................................24
     F3   Set EVENT/MISSION TIMERS ................................26
          Set MISSION/EVENT TIMERS ................................27
          Clear MISSION/EVENT TIMERS ..............................32
          Set SELECTED EVENTS .....................................32
          MISSION/EVENT TIMER NUMBERS .............................33
     F4   Set DAYLIGHT and Defaults ...............................34
          Set PAGE and TEXT Mode Delays ...........................34
     F5   Read or Save INI and MTD Files...........................36
          READ and SAVE INI Files .................................37
          READ and SAVE MTD Files .................................37
          INI Files from Other Locations ..........................39
     F6   Self-Calibration using TIMESET ..........................40
     F7   Switch TEXT Mode ........................................42
     F8   Switch PAGE Mode ........................................42
     F9   DOS SHELL (DOS 3.3+ ONLY) ...............................42
     F10  TIME SYNCHRONIZATION ....................................43
          Configuring Program TIMESET .............................43
          Time Synchronization Menu ...............................45
          VIEW or SET Time Sync Data ..............................45
          TIMESET Time Synchronization ............................45
          MANUAL Synchronization ..................................46
LAUNCH/HOLD SUPPORT ...............................................48
DOS CLOCK CALIBRATION .............................................50
     Setting DOS Time .............................................51
     Maintaining DOS Time .........................................52
     Calibrating DOS Time .........................................54
          Manual Hardware Clock Calibration .......................55
          Manual Software Clock Calibration .......................57
USING TEXT MODE ...................................................59
     Preparing TEXT Files .........................................60
Modifying JPLCLOCK.INI for Special Features .......................61
COMMENTS AND KNOWN PROBLEMS .......................................63
     Computer Processor and Math Coprocessor ......................63
     Computer BIOS Problems .......................................64
     Monitor Type and Video Adapter Cards .........................64
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page ii


     DOS Version and the Shell Feature ............................64
     Problems with IBM OS/2 .......................................65
     Unstable Hardware or Software Clocks .........................65
     Typical Calibration Results ..................................65
     Color Variations .............................................66
UTC AND TIME ZONES ................................................67
FUTURE IMPROVEMENTS AND FEATURES ..................................69
JPLCLOCK REVISION HISTORY .........................................70
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page ii



                    JPLCLOCK (NORMAL MAIN CLOCK SCREEN)

º JPLCLOCK by David H. Ransom, Jr.  Version 9401 º JD2449355.08333   2 JAN 1994
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NOTE: Pages ii and iii use the IBM "line drawing" characters as they appear
on the display screen. If your printer cannot print these characters, these
pages may appear garbled. These line drawing characters are not used
elsewhere in this documentation; instead, I substitute similar characters
from the normal character set.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page iii



                    JPLCLOCK (SMALL MAIN CLOCK SCREEN)

º JPLCLOCK by David H. Ransom, Jr.  Version 9401 º JD2449355.08635   2 JAN 1994
                                                                     þþþþþþþþþþ
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                                                   ³        -31   21:35:39    ³
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Ú[ CAN  Canberra ]ÄÄÄÄÄ¿  Ú[ MAD  Madrid ]ÄÄÄÄÄÄÄ¿ Ú[Retract Crew Access Ar]ÄÄ¿
³    3  01:04:21 AEST* ³  ³    2  15:04:21  CES  ³ ³        -31   21:58:09    ³
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NOTE: Pages ii and iii use the IBM "line drawing" characters as they appear
on the display screen. If your printer cannot print these characters, these
pages may appear garbled. These line drawing characters are not used
elsewhere in this documentation; instead, I substitute similar characters
from the normal character set.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 1


INTRODUCTION
------------

     JPLCLOCK is a clock and event timer program written at the request of
the JPL Flight Projects Support Office especially for use in the NASA Jet
Propulsion Laboratory's Multimission Computer Control Center (MCCC) in
Pasadena, California, and is continuously displayed on one of the five
large projection screens overlooking the MCCC. JPLCLOCK provides mission
controllers in the MCCC with current JPL time (Pacific Standard or Daylight
Time), UTC (Coordinated Universal Time), and DSN (Deep Space Tracking
Network) times as well as up to 60 selected mission or event timers. In the
event that the hard line to NIST in Boulder, Colorado, is out of service,
JPLCLOCK operates as the backup time standard for the MCCC. A text
presentation mode allows the display of supplementary text and other
messages when the program is used for more general applications.
     JPLCLOCK is copyrighted software; you are hereby granted a non-
exclusive license for non-commercial or educational use only. Agencies of
the United States Government are hereby also granted a non-exclusive
license for the use of this program. Use it if you like it, discard it if
you don't. There are no warranties of any kind. If you wish to use JPLCLOCK
commercially, write for license information.


JPLCLOCK FEATURES
-----------------

-    JPLCLOCK can turn an "ordinary" IBM-compatible personal computer into
     a precision clock, synchronized to the National Institute of Standards
     and Technology in Boulder, Colorado or to the U.S. Naval Observatory
     in Washington, DC.

-    When used with the NIST or USNO Telephone Time Service, JPLCLOCK can
     maintain its displayed time to an accuracy of 0.25 seconds or better
     over extended periods of time.

-    JPLCLOCK automatically and continuously compensates for the drift of
     the DOS software clock. If program RIGHTIME is active, JPLCLOCK lets
     RIGHTIME control hardware AND software clock adjustments.

-    JPLCLOCK can display your local time and Universal Coordinated Time in
     large, easy to read characters in its Main Window.

-    JPLCLOCK can display the local time at four additional locations
     around the world.

-    JPLCLOCK can automatically adjust itself and your DOS clock for the
     correct DAYLIGHT or STANDARD time for all U. S. time zones.

-    JPLCLOCK tracks as many as 60 different missions or events, displaying
     the Mission Elapsed Time or a countdown to Time Zero for each event.
     Mission/event times may range from -27 years to +274 years!

-    JPLCLOCK can display up to four special PRIORITY EVENT timers that
     automatically select events whose Time Zero is closest to the current
     time.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 2



-    All features and events are set by the user so that JPLCLOCK may be
     easily configured for each installation.

-    JPLCLOCK can present supplementary text information on as many as 10
     successive display screens for news and public information.


     JPLCLOCK Version 9126 was the first limited public release of the
program in June of 1991, after a number of beta versions tested by Charles
White at the NASA Jet Propulsion Laboratory. Thanks to Charles, a number of
interesting features were added to the early versions, bugs were detected
and squashed, and the program was tested in JPL's Multimission Computer
Control Center (MCCC) and elsewhere. Other interested individuals at JPL
have also evaluated the program, offered criticism and suggestions, and
researched some of the older mission times. Mike Gardner in Sunnyvale has
reviewed an early version of my documentation and offered his usual
constructive criticism. To all of these people, my thanks!
     Although my initial discussions at JPL envisioned a "simple" program,
JPLCLOCK is definitely NOT simple. The original idea was to adapt my
program ASTROCLK to the task required in the MCCC. I have indeed borrowed
freely from ASTROCLK (as well as from another of my programs, STSORBIT) and
this helped get the first versions up and running relatively quickly. As
usually happens, the project quickly grew in scope and complexity. Everyone
involved, myself included, had new ideas or suggestions. Equally
significant, the personal computer is hardly the ideal precision clock, yet
JPLCLOCK is intended for the JPL MCCC where accuracy is critical. Making
sure that JPLCLOCK will maintain the required accuracy has consumed
considerable time and thought. It wasn't long before the source included
thousands of lines of code and the documentation grew to over 40 pages. All
this in the space of a couple of weeks of my "spare time"!
     Given the clock drift and accuracy problems inherent in the design of
the typical IBM-compatible personal computer, JPLCLOCK would not have been
practical without the various time services provided by the National
Institute of Standards and Technology (NIST) and the U.S. Naval Observatory
(USNO). The NIST radio stations WWV and WWVH provide an inexpensive and
convenient means for "ordinary folks" to synchronize clocks and other
equipment. The NIST and USNO Telephone Time Services offer a high precision
standard time calibration source when such accuracy is required.
     For high precision, I recommend programs TIMESET by Peter Petrakis and
RIGHTIME by Tom Becker. TIMESET will precisely set the DOS hardware and
software clocks from NIST, USNO, several European time services, or a
computer using Petrakis' program TIMEGEN (which in turn may be synchronized
to a time service). RIGHTIME (Version 2.53 or later) precisely maintains
the DOS clocks and compensates for "cool" drift (computer OFF) and "warm"
drift (computer ON). Both programs have been extensively tested. TIMESET
may be automatically scheduled and called from within JPLCLOCK. JPLCLOCK
senses the presence of RIGHTIME and disables its internal clock adjustment
features when RIGHTIME is performing that task.
     Every effort has been made to assure that program JPLCLOCK performs
its task accurately and reliably. However, while no known errors of any
consequence remain, JPLCLOCK is still a young program and it is almost
certain that some bugs are yet to be discovered. In addition, there is
still much that can be done to further enhance JPLCLOCK, so new versions
can be expected from time to time. User comments, suggestions, and bug or
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 3


problem reports will be appreciated!
     Programs such as JPLCLOCK take many hours to develop and maintain.
While it is not required, I would appreciate your registration of the
program; the $10 donation is very nominal and will encourage me to continue
supporting the program. Registration information is in file README. The
only other request I make of users is that they take the time to complete
and return the confidential questionnaire in file README whether or not
they register. The questionnaire gives users a chance to offer comments and
suggestions, and lets me know that people use and appreciate JPLCLOCK.
     For those who are interested in our space program and who have access
to a modem, I recommend NASA's SpaceLink Bulletin Board System in
Huntsville, Alabama, (205) 895-0028, 300 to 9600 baud on 8 lines, available
twenty four hours per day. NASA SpaceLink, operated by the NASA Marshall
Space Flight Center, provides a wealth of information on NASA and its
projects. Orbital elements for a Space Shuttle mission are usually
available while a mission is in progress. In addition to educational
materials, general information on NASA programs and plans, news releases,
and graphics images from current and prior spacecraft missions such as
Voyager and Magellan, SpaceLink also provides current news and information
on missions in progress. Mission status reports for all active missions are
generated periodically. I regularly call SpaceLink and post files of
interest on my own bulletin board system (BBS).
     Special thanks to Charles White of the NASA/JPL Flight Projects
Support Office for his continuing comments and suggestions during the
development and testing of this program, as well as a fascinating visit to
the JPL Multimission Computer Control Center. Like many others, I consider
the Jet Propulsion Laboratory to be a unique national resource, unequaled
anywhere else in the world. JPLCLOCK is entirely "a labor of love", to
repeat a well-worn phrase; to see my software operating in the MCCC where
amazing projects such as Voyager and Magellan are controlled is sufficient
reward.
     A brief biographical note: I am a retired physicist and engineer who
spent all of his professional life in the world of electronics, data
communications and, more recently, computers. As a young man I was actively
involved in the early American space program as a contractor for the Jet
Propulsion Laboratory, working on projects such as Ranger and Mariner.
Perhaps as a consequence of these and the many other remarkable NASA
projects directed by JPL, my respect and admiration for The Lab and its
people practically knows no bounds. I was also involved with the Mercury,
Gemini, and Apollo projects and my interest in space has continued to this
day. My experience includes both hardware and software, and I designed and
implemented software professionally for many years with considerable
success.
     I have been writing software for IBM-compatible personal computers,
usually oriented toward space and astronomy, for a number of years. Since
1987 I have also maintained the RPV ASTRONOMY BBS, a free access bulletin
board system with an emphasis on space and astronomy. So successful has
my latest "hobby" become that it is threatening to overwhelm my bulletin
board system and consume all of my available time just answering the mail!
All of my programs are free although I do encourage users to register them
for a modest fee. If my software also serves to help spark the interest of
young people in science and technology or can be a learning tool at any
level, I will have more than achieved my purposes.
     Two of my programs, ASTROCLK and STSORBIT PLUS, have become widely
known around the world. ASTROCLK is an attempt to consolidate a
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 4


multiplicity of astronomy and time related programs into a single useful
computer tool. My desire to "keep in touch" with our Space Shuttle missions
led to the development of STSORBIT, a simulation of the large wall map in
Mission Control at the Johnson Space Center in Houston, Texas. STSORBIT
evolved into STSORBIT PLUS, a much enhanced version of the program, and
eventually found its way (several times) to JPL where it is now often
projected in the MCCC during Space Shuttle missions and for other Earth
orbiting missions. STSORBIT was the catalyst for JPLCLOCK.
     The initial versions of JPLCLOCK were written over a period of several
weeks in June of 1991 with close coordination with JPL. Even before the
program was "finished" (if such programs are EVER really finished!),
JPLCLOCK was being used during a planned power outage as the primary time
standard in the Multimission Computer Control Center. JPL has also made
JPLCLOCK available on JPL computer networks so that Lab personnel may have
access to current time and mission information. Other applications for the
program are being considered by the Public Affairs Office. More recently,
it has been installed at the Space Operations Center 34 at Falcon Air Force
Base in Colorado for use during launches on programs such as MILSTAR. How
useful or interesting it may be to others remains to be seen.
     For current space and astronomy programs and data, as well as the
current version of this program, call my RPV ASTRONOMY BBS bulletin board
system which I maintain as a public service. There is no cost except for
the telephone call. The system has about 2000 more or less regular callers
and is often busy, so please be patient. If the BBS has not answered after
the third ring, hang up, wait TWO MINUTES, then call back; the system has
a power controller and if the system is off it takes that long for the
computer to start up and do its initial housekeeping chores.
     If you do not have access to a modem, you may send US$10.00 as a
donation for a copy of the current version of JPLCLOCK on disk; please
specify the disk size: 5-1/4" 360K or 3-1/2" 720K.
     JPLCLOCK can be a complex program when all of its features are used,
perhaps more complex than was originally anticipated. This documentation
attempts to completely describe the program and its operation. There may be
errors in this documentation, but please read it BEFORE you drop me a nasty
note or give up! Comments and suggestions are welcome.

                                   David H. Ransom, Jr.
                                   7130 Avenida Altisima
                                   Rancho Palos Verdes, CA 90274

                                   January 1994
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 5


PROGRAM DESCRIPTION
-------------------

     The NASA/JPL Multimission Computer Control Center (MCCC), located at
the Jet Propulsion Laboratory in Pasadena, California, is the "nerve
center" where all NASA planetary missions and some Earth orbiting missions
are controlled. Other NASA and ESA (European Space Agency) missions may
also be supported by MCCC from time to time. The Control Center resembles
other similar installations with consoles for each of the controllers and
other responsible individuals directing the progress of a mission and
coordinating the operation of the NASA Deep Space Network and other
critical resources. Operations continue around the clock with a number of
missions typically active. Missions active at this time include Voyager 1
and 2, Magellan, Ulysses, and Galileo.
     Above the main floor of the Control Center and in plain view of all
controllers and individuals in the visitors gallery are seven projection
screens, five large and two slightly smaller. JPLCLOCK is dedicated to one
of these large screens. The remaining screens display television or
computer generated images related to missions in progress or other images
and programs as selected by Control Center personnel. For example, NASA
Select Television is normally displayed when it is broadcasting.
     JPLCLOCK displays various time information for the convenience of
Control Center personnel. The current local time (Pacific Standard/Daylight
Time) and Coordinated Universal Time (UTC, or GMT as it was formerly
designated) are displayed in large characters in the program's main window.
Below that window are four smaller windows displaying local time at the DSN
locations or other selected installations. On the right side of the screen
are six smaller windows which display the Mission Elapsed Time for selected
missions in progress (green background) or Countdown Time for missions or
events due to occur (red background). The background color switches from
red to green when the countdown reaches zero or the event occurs. As many
as 60 different missions or events may be monitored with these timers.

                              IMPORTANT NOTE
                              --------------

          Before using program JPLCLOCK in applications requiring
          high accuracy, read the section DOS TIME CALIBRATION in
          this documentation!

     JPLCLOCK may be operated in two modes: NORMAL and PAGE. The NORMAL
mode displays the main window, four location time windows, and from one to
six timer windows continuously. If more than six timers have been
programmed, the user may select the timer "page"  to be displayed. Each
timer page displays a maximum of six timers. The PAGE mode displays the
same main window and four location windows but sequences automatically
through up to 60 different timer windows using ten different timer "pages".
The timer page is normally switched every thirty seconds; however, when any
timer on a particular page is within one hour of of "Time Zero", the
display will "freeze" on that timer page. As long as events which occur
within several hours of one another are arranged on the same screen page,
JPLCLOCK will automatically ensure that the timer for each event is
displayed from one hour before to one hour after Time Zero.
     In addition, up to ten screen pages of supplementary text information
or messages may be displayed in conjunction with the PAGE mode. When the
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 6


TEXT mode is active, the program cycles through all of the active timers
then switches and presents the text pages in sequence. This real time to
text to real time sequence repeats indefinitely unless an active timer
reaches the plus or minus one hour period around its Time Zero, in which
case that timer page freezes as described above.
     The default JPLCLOCK configuration is arranged for the convenience of
the Jet Propulsion Laboratory MCCC. One or more initialization files, files
with a file type ".INI" and containing alternate or supplementary time and
location data, may also be included from time to time. Manual configuration
features are included for setup at other locations. Window titles, mission
or event names, and window times are easily configured for the desired
location or event. Inactive location or timer windows may be removed from
the screen. The current configuration is saved each time JPLCLOCK is run so
that the program may be resumed at any time. While the program is running,
all keyboard operations are timed so that inattention on the part of the
user for more than ten to thirty seconds (depending upon the operation
being performed) will result in automatic restarting of the program.
     JPLCLOCK is intended for a dedicated IBM-compatible computer running
MS-DOS version 3.3 or higher. Best performance will be achieved using a 286
or better processor equipped with a math coprocessor chip. However, the
program should execute correctly (but perhaps with perceptible delays)
using any IBM-compatible computer with or without a math coprocessor chip.
For normal use, the program should started from the computer's AUTOEXEC.BAT
file so that it is restarted in the event of a power failure.
     As of June 1991, JPLCLOCK is still a relatively new program. Although
all known problems have been corrected, there are doubtless a few minor
bugs yet to be discovered. User comments and suggestions are welcome.
Future versions are anticipated at periodic intervals as new features are
added and/or problems are corrected. Planned features include optional
automatic synchronization with compatible external time signals.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 7


JPLCLOCK HARDWARE AND SOFTWARE REQUIREMENTS
-------------------------------------------

     JPLCLOCK is written for use on IBM-compatible computers using the
Microsoft DOS operating system, Version 3.3 or higher, and has been tested
primarily on computers equipped with an 80286 or higher processor. For
critical applications, the minimum hardware configuration is a computer
equipped with an 80286 processor AND an 80287 math coprocessor. An EGA or
VGA color display is recommended.
     Most of JPLCLOCK's features should operate correctly on older XT class
computers but those features which use the clock/calendar chip, introduced
with the AT-class computer and subsequently retrofitted to older computers
as an add-on chip or circuit card, may not operate correctly. Several
different clock chips have been used on PC and XT machines which are NOT
compatible with the AT chip and may not be compatible with JPLCLOCK or
program TIMESET. Program RIGHTIME requires an AT-class computer, 80286 or
higher.
     JPLCLOCK requires a modest amount of the computer's memory. The
program has not been tested on a machine with less than 640K of main RAM.
Although most JPLCLOCK operations are entirely memory resident, program
startup, use of program TIMESET, and the DOS shell all require disk
accesses. Because of the excessive time delays associated with floppy disk
drives, a hard disk is strongly recommended. Even with a hard disk, delays
and system software vary considerably and performance may differ from
system to system and from drive to drive.
     Operation of JPLCLOCK on computers without a math coprocessor is
possible but may be marginal on some older XT and AT class computers.
Typical symptoms of a "slow computer" are skipping seconds and a "ripple"
effect visible as the clocks and timers are updated on the screen. A number
of users have reported problems on these computers, especially when not
equipped with a math coprocessors. See the section COMMENTS AND KNOWN
PROBLEMS, "Computer Processor and Math Coprocessor", for discussion and
suggestions.
     JPLCLOCK assumes DOS Version 3.3 or higher; MS-DOS and PC-DOS are
considered equivalent and referred to as "DOS" although testing has been
performed only on systems using MS-DOS. All testing has been performed with
Versions 3.3+ and 5.0. The DOS Shell feature, required for the use of
program TIMESET, is considered unreliable for versions of DOS prior to DOS
3.1. If you have not upgraded to at least DOS 3.3 (DOS 5.0 recommended!),
consider doing so!
     Not surprisingly, JPLCLOCK relies upon the internal clock in your
computer to maintain accurate time. However, not all computer clocks are
created equal; some are much more accurate than others and it is difficult
to predict that performance in advance. The computer clock was simply not
designed as a high precision timekeeping instrument. Further, recent
versions of DOS (3.3 and higher) can reset an otherwise relatively accurate
hardware clock if the software clock loses time.
     Just as your quartz watch will keep time most consistently (as opposed
to accurately) when you leave it always on your wrist, so too your computer
clock will keep time best if it is left on continuously. Voltage, time and
temperature changes are a quartz oscillator's worst enemies, along with a
long term crystal aging effect. Taken together, these effects can cause
your clock to lose or gain up to several seconds per day. For reasonably
accurate operation, your computer clock should be synchronized against a
time standard from time to time. See the sections DOS CLOCK CALIBRATION and
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 8


TIME SYNCHRONIZATION for additional discussion, especially for
installations where high precision is desired or required.
     For those individuals willing to modify their computer's hardware,
Mike Gardner has written a short memo, CLKFREQ.TXT, which describes a
simple hardware modification for some PC clocks which can improve their
accuracy by at least an order of magnitude. A variable capacitor is part of
the circuit and permits physical calibration of the clock frequency to
external standards. NOTE: Modification of your computer may affect its
warranty; read your warranty and CLKFREQ.TXT before you make ANY hardware
modifications.
     Other factors may also affect the accuracy of the computer's clock.
One of the most common and severe offenders is Local Area Network (LAN)
software; while this can vary depending upon the LAN BIOS and network
hardware being used, the networking software in many systems may completely
or partially ignore the clock's "time ticks" during network operations.
Another frequent offender is high speed communication (usually about 50Kb
per second or higher) via the serial communications ports, COM1 through
COM4; in this case too, time ticks may be lost and the clock will fall
behind. Clock problems related to networking or other software can result
in time losses up to tens of seconds or even minutes per day! There is no
remedy for this situation except: a) avoid using the software which causes
the problem; or b) use program RIGHTIME to continuously adjust the DOS
clocks.
     The performance of the DOS software clock can vary considerably from
computer to computer and from one version of DOS to another. It may also be
sensitive to certain software. Avoid using your favorite TSR (Terminate and
Stay Resident) programs when running JPLCLOCK. Several hours of operation
with JPLCLOCK will establish whether or not your computer and DOS software
clock are suitable for use with the program. If the either the hardware or
software clock is unstable or varies too much with time or temperature, it
may be unsuitable for use with JPLCLOCK. There is no remedy in most cases
except to use a different computer with a better clock.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 9


JPLCLOCK FILES
--------------

     JPLCLOCK is normally distributed in archived (compressed) format. The
following files are usually included:

          JPLCLOCK.EXE        Main program          (required)
          JPLCLOCK.DOC        Documentation         (not required)
          JPLCLOCK.INI        Initialization data   (optional)
          JPLCLOCK.MTD        Mission Timer Data    (optional)
          JPLCLOCK.MSG        Sample TEXT file      (optional)
          JPLFONT.COM         Experimental EGA font (optional)
          STANDARD.INI        Copy of JPLCLOCK.INI  (optional)
          STANDARD.MTD        Copy of JPLCLOCK.MTD  (optional)
          README              Program Registration  (not required)
          FILE_ID.DIZ         Brief description     (not required)

JPLCLOCK.EXE, noted as "(required)", must be in the current default
directory for program operation. Files noted as "(optional)" do not need to
be in the default directory when JPLCLOCK is operated but may provide
additional features or information if present. File JPLCLOCK.MTD contains
data for selected missions. If file JPLCLOCK.INI is not present, it will
automatically be created the first time the program is executed. Files
STANDARD.INI and STANDARD.MTD are backup copies of the corresponding
JPLCLOCK files.
     Additional MTD files (files with filetype ".MTD", standing for
"Mission Timer Data") may be included from time to time with interesting or
upcoming events pre-programmed. Other MTD files may be posted periodically
on my bulletin board system for upcoming events.
     Registration of program JPLCLOCK is not required but certainly will be
appreciated! The modest donation is only US$10.00! See the file README for
registration information. JPLCLOCK has involved considerable effort to
develop and test, and your registration will encourage me to continue
enhancing and supporting the program. As a "bonus" for registration, I will
send the current version of JPLCLOCK to you on disk; please specify the
disk size desired: 5-1/4" 360K or 3-1/2" 720K (supplied if no disk size
specified).
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 10


Programs TIMESET and RIGHTIME
-----------------------------

     Two fine programs, TIMESET by Peter Petrakis and RIGHTIME by Tom
Becker, provide all the features required to accurately set and maintain
the computer's hardware and software clocks. Development efforts on these
programs have been carefully coordinated so that they cooperate with each
other. Both programs are copyrighted commercial software distributed as
"shareware" and require registration after an initial evaluation period. I
highly recommend these programs and encourage users to support the authors
and their work. So far as I know, there are no other comparable programs
available at any price!

TIMESET, Version 7.20, uses the telephone time services of NIST, USNO, and
three European services to precisely set the computer clocks. The standard
distribution also includes several additional time-related utility
programs. It is available on many computer bulletin board systems or direct
from:

          Peter Petrakis
          Life Sciences Software
          8925 271st N.W., Suite 112
          Box 1560
          Stanwood, Washington  98292  USA

          Telephone: (206) 387-9788

RIGHTIME, Version 2.5+, is a program to compensate for the various drift
factors in a computer's hardware and software clocks. When used in
conjunction with TIMESET and properly calibrated, RIGHTIME "learns" the
warm and cool drift factors for a specific computer. As a result, the
clock's can be maintained with an accuracy of a fraction of a second over
long periods of time. It is available on many computer bulletin board
systems or direct from:

          Tom Becker
          Air System Technologies, Inc.
          14232 Marsh Lane, Suite 339
          Dallas, Texas  75234  USA

          Telephone: (214) 402-9660

Tom Becker also operates a TIMEGEN service which emulates the USNO Time
Service and which provides a time service typically accurate to within 0.01
seconds. Callers (especially those in the Southwest) may use TIMESET to
call the TIMEGEN service and set their computer clocks with essentially the
same accuracy as calling USNO or NIST.

          Air Systems Technologies TIMEGEN SERVICE
          (214) 869-0344

Tom Becker and Peter Petrakis may be also contacted directly on the Air
Systems Technologies computer bulletin board system in Dallas, Texas. The
BBS always has the latest versions of TIMESET and RIGHTIME available for
download:
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 11



          Air Systems Technologies BBS
          (214) 869-2780

     JPLCLOCK is now "aware" of program RighTime and its use is recommended
for accurate timekeeping. JPLCLOCK/s internal time adjustments are disabled
when RighTime is detected.


                               *************
                               *  CAUTION  *
                               *************

     JPLCLOCK expects RighTime Version 2.5+; performance with prior
     versions of RighTime may yield unpredictable results.


     The following descriptive text is extracted with permission from the
documentation for the current versions of TIMESET and RIGHTIME; please
consult the documentation for each program for full details. Although
future versions of both programs are expected to remain compatible with
JPLCLOCK, they should be tested carefully before regular use.


FEATURES OF TIMESET 7.20
------------------------

     TimeSet has been evolving steadily ever since the first version was
released in the summer of 1987.  That version and several subsequent ones
could only set a computer's clock from the U.S. Naval Observatory (USNO) in
Washington, D.C.  Version 6.00, released in 1990, added ability to use
telephone time signals from the National Institute of Standards and
Technology (NIST) in Boulder, Colorado, making it the first program of its
kind able to address more than one atomic time service.  This made it
possible for computer users in the eastern and western United States to
keep down long distance bills by choosing the time service closest to them.
     Version 7.10 continues that evolution with a number of new features
and supporting utilities:

o    TimeSet can now access five atomic clock-based telephone time services
     on two continents: the USNO and the NIST in the United States, as
     before, and atomic time services in Sweden (National Time and
     Frequency Laboratory), Austria (Technical University of Graz), and
     Italy (National Electrotechnical Institute).  People in European
     countries who want to set their computers to an atomic clock no longer
     need to make a trans-Atlantic phone call.

o    TimeSet 7.10 is designed to interact closely with version 2.5+ of
     RighTime (tm), the excellent memory-resident regulator for computer
     clocks developed by Tom Becker of Air System Technologies, Inc.,
     Dallas.  RighTime learns the drift rate in the computer's clock and
     continuously applies a correction to compensate for it, and it refines
     the correction each time the computer clock is set.  A computer with
     RighTime installed and trained can maintain system clock accuracy
     within a second for at least a week. Furthermore, version 2.46
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 12


     provides true 0.01-sec resolution in the DOS clock, in contrast to the
     normal 0.055-sec resolution.  This allows greater accuracy in
     timesetting than ever before, indeed the maximum accuracy that can be
     obtained with a computer clock.  Life Sciences Software and Air System
     Technologies cooperated closely during the development of TimeSet 7.10
     and RighTime 2.46, with the result that TimeSet can access several
     RighTime functions directly.

"TIMESET" is a trademark of Life Sciences Software (TM)

The following is a screen dump of the data displayed by TIMESET:

+------------------- From NIST.  Connect time: 10.43 sec. --------------------+
| DATA FOR TIME CALCULATIONS (all data pertain to Coordinated Universal Time) |
|    Time data string:  49187 93-07-19 00:27:51 50 0 +.6 053.8 UTC(NIST)      |
|                Date:  07-19-1993                                            |
|         Julian date:  2449187                                               |
|         Day of year:  200                                                   |
|                Hour:  00    Minute:  27    Second:  51                      |
|                   Daylight Time is in effect in the U.S.                    |
|        U.S. Standard Time begins on 10-31-1993 at 02:00:00 local time.      |
+-----------------------------------------------------------------------------+
                                                 System clock set: 17:27:51.01 
+-----------------------------------------------------------------------------+
| --------------- ACTION SUMMARY (at instant of timesetting) ---------------- |
|    Internal delay adjustment:  .01 sec. (added to set time)                 |
|        Line delay adjustment:  .0538 sec. (precompensated by time service)  |
|                                                                             |
|   Universal Time Coordinated:  00:27:51.01           (time at 0ø longitude) |
|                     UTC Date:  07-19-1993, Monday    (date at 0ø longitude) |
|                                                                             |
|      Local computer time was:  17:27:49.53                                  |
|                       Set to:  17:27:51.01 Pacific Daylight                 |
|      Local computer date was:  07-18-1993                                   |
|                       Set to:  07-18-1993, Sunday, Day 199 of 1993          |
+-----------------------------------------------------------------------------+


FEATURES OF RIGHTIME 2.5+
-------------------------

     RighTime brings exceptional system time of day clock performance to
the DOS-based AT-class-compatible PC computer with no additional hardware. 
With RighTime installed, the standard real time clock system becomes an
Adaptive Mathematically Compensated Crystal-controlled Oscillator based
clock.  Under stable conditions, RighTime can produce a system clock that
keeps time within one half second per week or better (some testers have
reported accuracy of 0.07 second per week); this is about 0.8 parts per
million error, or more than 100 times better than an unconditioned crystal
time base alone, or 30 times better than a moderately conditioned one like
a modern watch of quality.

o    True one hundredth second DOS clock resolution: the 55-millisecond
     barrier is broken!  The standard DOS clock resolves to only about 1/18
     second; under RighTime v2, the new high resolution DOS clock resolves
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 13


     to, and increments in, hundredths while the Int 08h and 1Ch tick rate
     remains standard.

o    RighTime intrinsically sets the hardware clock and solves the midnight
     rollover date bug that exists in some DOS versions; this eliminates
     the need for other utility programs or drivers that perform these
     functions.  Unlike DOS alone, the hardware clock seconds transition
     will be properly set by RighTime and the time will be set to
     hundredths of a second resolution, and these qualities will survive
     through rebooting.

o    Each time you set the time, RighTime will improve the accuracy of the
     clock error corrections and will subsequently improve the accuracy of
     the clocks.  It should be easy to achieve a worst-case error of less
     than 0.5 second per day and under good conditions, less than 0.5
     second per week; typical results are much better.  Command line
     options are provided that allow fine tuning the correction process to
     your system.  A trimming option provides for offset adjustments in
     hundredths of a second.

The following is a screen dump of the data displayed by RIGHTIME:

RighTime: Indicated DOS clock date and time is 1993/03/05 06:04:45.66.
RighTime: Warm correction rate is +2.83 seconds per day.
RighTime: Cool correction rate is +4.27 seconds per day.
RighTime: Current applied DOS-CMOS RTC offset is +0.46 second.
RighTime: Last CMOS RTC adjustment was 0.00 hours ago.
RighTime: Last timeset was 23.33 hours ago.
RighTime: System has been warm 17% of the time since the last timeset.
RighTime: Stack A headroom is 92 bytes; Stack space used is 68 bytes.
          Stack D headroom is 100 bytes; Stack space used is 60 bytes.
RighTime: /?=Help; Version 2.54
RighTime: Copyright 1991-93 GTBecker, Dallas 214/402-9660. All Rights
          Reserved.
RighTime: Resident and enabled.
RighTime: Selftest passed.
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 14


STARTING PROGRAM JPLCLOCK
-------------------------

     Before starting program JPLCLOCK for the first time, make sure that
all required files are in the current drive and directory (see the file
information on the previous page). Delete the file JPLCLOCK.INI if it has
been created by a previous version of JPLCLOCK or you are using the program
at a different location from the one which prepared the file. The format of
the INI file may change with new versions and, although the program may
read prior versions of .INI files, it is safer to "start from scratch". The
INI file also includes specific information related to the local time zone.
     To start program JPLCLOCK for operation in the NORMAL mode, enter the
following command at the DOS prompt:

          JPLCLOCK

The file JPLCLOCK.EXE has been compressed to save disk space using program
PKLITE by PKWare and there may be a modest delay before the program begins
operation. As described in the summary of command line options below, you
may add the "/M" command line option to force monochrome operation on CGA,
EGA, and VGA systems.


JPLCLOCK Command Line Options
-----------------------------

     All JPLCLOCK program features (except monochrome operation) may be
enabled or disabled from within the program. However, to facilitate use
with batch files, certain features may be enabled using "command line
options", specific words preceded by the slash ("/"), used when the program
is started from the DOS prompt. A command line consists of the program name
followed by the desired command line option(s): "JPLCLOCK [option] ...
[option]". The following command line options are available:

     ?         (Special option) Displays brief help information to remind
               users of the principal command line options and then returns
               to DOS.

     /M        Force monochrome operation. On color monitors, this usually
               forces white or light white on black background.

     /SMALL    Enables the SMALL main clock window and the additional four
               SELECTED/PRIORITY timer windows.

     /PAGE     Enables PAGE mode operation with up to 60 Mission/Event
               Timers displayed in "pages" of six timers each. Default is
               the non-page mode with only 6 Mission/Event Timers.

     /TEXT     Enables TEXT (and PAGE) mode operation if file JPLCLOCK.MSG
               is found. Up to ten screen pages of prepared text may be
               sequentially displayed.

     /FAFBnn   Enables MET in SECONDS for Event Timer #nn where "nn" must
               be a 2-digit number between 01 and "60" and point to an
               active Event Timer from which MET is to be calculated. For
Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 15


               example, to calculate MET from Event Timer #37, use the
               command line option "/FAFB37". When enabled, MET replaces
               the Julian Date normally displayed at the upper right of the
               screen. (Special Feature for Space Operations Center 34,
               Falcon Air Force Base, CO.)

Setting UTC Zone and Daylight Flags
-----------------------------------

     JPLCLOCK must know the correct local time and time zone in order to
operate accurately. In addition, your computer clock may be set either to
LOCAL time or to Coordinated Universal Time (UTC). The first time JPLCLOCK
is executed (or any time the program cannot find the file JPLCLOCK.INI),
the program prompts you for this information:


Set UTC TIME ZONE OFFSET and DAYLIGHT FLAG

JPLCLOCK must know the difference between your local time zone and Universal
Coordinated Time (UTC), also sometimes known as Greenwich Mean Time (GMT).
In addition, JPLCLOCK must know if your local time zone is now using STANDARD
or DAYLIGHT (SUMMER) time and if your computer is set to LOCAL or UTC time.

First, enter the difference between your STANDARD time zone and UTC in hours.
Do NOT include the hour for daylight time if you are now on DAYLIGHT time;
it will be entered separately. For most time zones in the United States and
Canada, the entries required are:

  Eastern Standard Time     EST    -5.00
  Central Standard Time     CST    -6.00
  Mountain Standard Time    MST    -7.00
  Pacific Standard Time     PST    -8.00

Enter UTC Offset (hours) [ -8.00]:              -8.00
Enter Daylight Flag (0=OFF, 1=ON, A=AUTO) [1]:  ON, AUTOMATIC
Enter DOS Time (0=LOCAL, 1=UTC)
  • :            LOCAL

    Press ENTER to ACCEPT, any other key to repeat:


         The example entries shown above illustrate the required information
    for Pacific Daylight Time: "-8" for the standard time zone offset from UTC,
    "ON,AUTOMATIC" to signify that automatic Daylight Time is in effect, and
    "LOCAL" to show that the computer is set to local time rather than UTC
    time. Enter the information that is appropriate for your time zone and
    computer clock, then press ENTER when the information is correct. Press
    any other key to repeat the process. If an item is correct as shown within
    the square brackets ([...]), you may press ENTER to skip that item and
    leave it unchanged. In order to set Daylight Savings Time to ON and to
    AUTOMATIC, set the Daylight Flag to ON the first time then repeat and set
    to AUTOMATIC the second time. These data are saved in file JPLCLOCK.INI and
    will not be requested again.
         When the Daylight Flag is set to AUTOMATIC, the program will
    automatically switch the program AND the DOS clock from and to Daylight
    Savings Time on the last Sunday in October and the first Sunday in April
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 16


    in accordance with U. S. convention. Locations outside the United States
    which do not observe the same convention must switch the Daylight Flag
    manually using F4+F1 from the Main Menu.
         The Daylight Flag controls the selection of Standard or Daylight
    Savings Time for the main clock display and all Location Timers which are
    set to use U. S. Daylight Savings Time. When used in the Automatic mode,
    the time and date of the change is correct for the local time zone.
    However, since all time zones are switched simultaneously, the time and
    zone abbreviation for other time zones using Daylight Savings Time will be
    incorrect for as much as several hours. For example, if Automatic Daylight
    Savings Time is enabled and the local time zone is Pacific, a Location
    Timer in the Central time zone set to use DST will change to or from
    Daylight Savings Time two hours late. Location Timers which are NOT set to
    use DST must be adjusted manually from the Main Menu.
         Once this information is set, JPLCLOCK continues with its normal
    startup and displays the title screen (see below). Verify that the current
    local and UTC time and date (including your local time zone abbreviation if
    you are located in the United States) are correct before proceeding.
    JPLCLOCK will start automatically in 10 seconds and the message on the
    screen will count down during the wait time. No operator action is required
    if you wish JPLCLOCK to start; you may also press ENTER twice to
    immediately start the program, bypassing the 10 second delay.
         JPLCLOCK's full name and the current version are shown on the title
    screen, followed by the current time and date. At this point the program is
    awaiting user input; if no keyboard input is detected within 10 seconds,
    the program will automatically begin operation. Press ENTER to display the
    Main Menu or ESC to quit the program and return to DOS. All other keys are
    ignored except that a timed message is displayed at the upper right of the
    screen reminding the user to press ENTER for the Main Menu. When program
    RIGHTIME is not active, the following title screen will appear:
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 17



                                    Program JPLCLOCK

                  NASA/JPL Multimission Computer Control Center Clock
                                      Version 9401


                       Current time:  15:30:02 PDT   22:30:02 UTC
                       Current date:    07/19/1993     07/19/1993


                    JPLCLOCK will start automatically in 10 seconds

                                           OR

                            Press ENTER for MENU, ESC to QUIT



                  (C) Copyright David H. Ransom, Jr., 1991-1993
                                  All rights reserved.


    When program RIGHTIME (Version 2.53 or higher) is detected, the time
    information will be supplemented:


                           DOS time:  15:30:02.87      07-19-1993
                          CMOS time:  15:30:02         07-19-1993
                       Current time:  15:30:02 PDT   22:30:02 UTC
                       Current date:    07/19/1993     07/19/1993
                            RighTime Version 2.54 detected!


         Note both the local time and date (Pacific Daylight Time in the
    examples) and UTC time and date (Coordinated Universal Time). Be sure that
    ALL time and date items are correct. If not, press ENTER to go to
    JPLCLOCK's Main Menu and then press F4 to correct the information.


                                  IMPORTANT NOTE
                                  --------------

              If you are using a JPLCLOCK.INI file (or any other INI
              file) prepared at some other location, your local time
              and date may not be correct. If all else fails, quit
              program JPLCLOCK, delete file JPLCLOCK.INI, and restart
              the program. JPLCLOCK will assist you in setting up the
              program for your time zone and will create a new
              JPLCLOCK.INI file for subsequent use.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 18


    JPLCLOCK MAIN CLOCK DISPLAY
    ---------------------------

         The Main Clock display for JPLCLOCK is illustrated on Pages ii and iii
    above. Two screen layouts are available, selectable either by a command
    line option or by a Function Key, NORMAL or SMALL. The NORMAL screen
    provides a large window with special large characters for Local and UTC
    Times and is recommended when the program will be used on a normal monitor
    which may have to be viewed from some distance. The SMALL screen provides a
    smaller window for Local and UTC Times along with up to four additional
    timers and may be preferred when JPLCLOCK is projected on a large screen.
         The remaining windows are the same for both screen layouts. The four
    Location Clocks are below the main window, and the six Mission/Event Timers
    are on the right side of the screen. The Location Clocks and the
    Mission/Event Timers are separately described in following sections. In
    addition to these data, the main clock display also includes the program
    name and version, as well as the current Julian Date (a standard method of
    day numbering used by scientists and astronomers) and local date (day-
    month-year) at the upper right corner of the display.
         The following keys are active while JPLCLOCK is running and the clocks
    and timers are displayed on the screen:

              ENTER     Stop the main clock display and go to JPLCLOCK's Title
                        Screen. Press ENTER again to go to the Main Menu. See
                        the section below for a description of the available
                        commands at the Main Menu.

                ESC     Quit JPLCLOCK and return to DOS. You will be asked to
                        press ESC again to confirm that you wish to quit the
                        program. If not, press ENTER to resume operation.

             ALT-F1     Freeze the display. Updating the screen stops EXCEPT
                        that Local and UTC Time will be updated above the Main
                        Window and the word "FREEZE" will flash in yellow above
                        the Mission Timer Windows while the freeze is in
                        effect. The freeze will be automatically released in
                        five minutes, or press ENTER to release the freeze
                        immediately. (Actually, pressing any key except keys
                        which do not generate a character, such as SHIFT, ALT,
                        or CTRL, will release the freeze.)

             ALT-F2     Enable or disable automatic SCREEN BLANKER. When
                        enabled, the screen blanker will clear the computer
                        screen five minutes after the last keystroke. The
                        screen will also be displayed for five minutes at 29
                        and 59 minutes past the hour. Press ENTER to display
                        the screen when it is blanked. (Actually, pressing any
                        key except keys which do not generate a character, such
                        as SHIFT, ALT, or CTRL, will cause the screen to be
                        displayed.)

             ALT-F5     Change SELECTED/PRIORITY EVENTS display. This key is
                        active ONLY when the SMALL Main Window is active. The
                        choices are: four SELECTED Mission Timers; two SELECTED
                        Mission Timers and two PRIORITY Mission Timers; or,
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 19


                        four PRIORITY Mission Timers. Press again for the next
                        arrangement.

             ALT-F6     Switch between the LARGE Main Window and the SMALL Main
                        Window. Enabling the SMALL Main Window also displays
                        the four SELECTED/PRIORITY Event Timers (as currently
                        selected).

             ALT-F7     Enable LAUNCH/HOLD SUPPORT mode. This mode enables the
                        user to adjust a group of Mission/Event Timers for
                        mission or launch delays, keyed upon a single Key
                        Timer, in real time. All affected timers are "frozen"
                        while in the LAUNCH/HOLD SUPPORT mode until ALT-F7 is
                        pressed again at the appropriate moment at which time
                        JPLCLOCK returns to normal operation. See the section
                        LAUNCH/HOLD SUPPORT for additional information.

             ALT-F8     Enable or disable the PAGE and TEXT modes. If no
                        command line options are specified, the default mode is
                        both PAGE and TEXT modes disabled. Each time ALT-F8 is
                        pressed, JPLCLOCK switches between PAGE and TEXT
                        disabled, PAGE enabled, and TEXT enabled. This command
                        combines the functions of F7 and F8 on the Main Menu.

             ALT-F9     EXPERIMENTAL COMMAND to enable a special screen font,
                        similar to "Helvetica", for EGA and VGA monitors ONLY.
                        Press ALT-F9 to enable the special screen font and
                        large numbers in the time displays; press ALT-F9 again
                        to use "normal" size characters in the time displays.

                        The special font is designed primarily for EGA systems
                        and may not operate correctly on some VGA systems. (On
                        one VGA system, for example, the last few lines of the
                        screen show a variety of text and graphics symbols when
                        program TIMESET is executed, and these symbols remain
                        on the screen when JPLCLOCK resumes operation.)

            ALT-F10     Immediately perform TIME SYNCHRONIZATION using the
                        external program TIMESET to call either the National
                        Institute of Standards and Technology (NIST) or the
                        U.S. Naval Observatory (USNO). See the section TIME
                        SYNCHRONIZATION for further information on this command
                        and program TIMESET. This command is the same as the
                        F10+F1 commands on the Main Menu.

               PgUp     ONLY ACTIVE IN THE NORMAL MODE. Allows the user to page
                        UP (increasing page number) through the active timer
                        pages. Inactive timer pages will be automatically
                        skipped.


               PgDn     ONLY ACTIVE IN THE NORMAL MODE. Allows the user to page
                        DOWN (decreasing page number) through the active timer
                        pages. Inactive timer pages will be automatically
                        skipped.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 20



         Four additional timer windows appear on the screen below the Main
    Clock window when the SMALL Main Window is selected. These are divided into
    two classes: SELECTED EVENTS and PRIORITY EVENTS. SELECTED EVENTS are just
    like regular Mission/Event Timers except that they are always displayed;
    they may be selected from the current Mission/Event Timers by pressing
    F3+F2 from the Main Menu. PRIORITY EVENTS are those events which have a
    Time Zero which is within 24 hours of the current time.
         Three different arrangements of SELECTED EVENTS and PRIORITY EVENTS
    may be selected by pressing ALT-F5 when the SMALL Main Clock is displayed.
    These two classes of events are always selected from the available 60
    Mission/Event Timers; note that the titles have been truncated because the
    window width is shorter than the normal Mission/Event Window. The default
    arrangement displays four SELECTED EVENTS:

              +--------------- SELECTED EVENTS ----------------+
              |                                                |
              +[Hubble Space Telesc]-+  +[ Voyager 1 ]---------+
          #1  |    424  01:38:02     |  |  5,051  01:13:54     |  #3
              +-----------------------  +----------------------+
              |                                                |
          #2  +[Gamma Ray Observato]-+  +[ Voyager 2 ]---------+
              |     90  22:49:09     3  3  5,066  23:47:54     |  #4
              +----------------------+  +----------------------+
              +------------------------------------------------+

         Pressing ALT-F5 once will change the arrangement to two SELECTED
    EVENTS and two PRIORITY EVENTS:

              +-- SELECTED EVENTS ---+  +-- PRIORITY EVENTS ---+
              |                      |  |                      |
          #1  +[Hubble Space Telesc]-+  |                      |  #1
              |    424  01:37:27     |  |                      |
              +----------------------+  |                      |
              |                      |  |                      |
          #2  +[Gamma Ray Observato]-+  |                      |  #2
              |     90  22:48:34     |  |                      |
              +----------------------+  |                      |
              +----------------------+  +----------------------+

    Note that only the first two SELECTED EVENTS are now displayed. In this
    example, there are no active PRIORITY EVENTS and therefore that window area
    is blank. JPLCLOCK continuously scans all 60 Mission/Event Timers to
    determine if any are less than 24 hours (plus or minus) from the current
    time. Events which have not yet occurred are shown with a RED background
    and a minus sign ("-") before the days, and events which have already
    occurred are shown with a GREEN background. If any events are found within
    the 24 hour range, they are sorted every second in such a way that #1 is
    that event now closest to Time Zero and #2 is the next closest to Time
    Zero. The ordering of PRIORITY EVENTS is set dynamically and will change as
    the time difference between the Time Zero set in the Mission/Event Timers
    change with respect to current time.
         Pressing ALT-F5 again will change the arrangement to four PRIORITY
    EVENTS:

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 21


              +--------------- PRIORITY EVENTS ----------------+
              |                                                |
              +[ Test Event ]--------+                         |
          #1  |      0  01:38:02     |                         |  #3
              +-----------------------                         |
              |                                                |
          #2  |                                                |
              |                                                |  #4
              |                                                |
              +------------------------------------------------+

    As described above, the PRIORITY EVENTS are continuously scanned and
    sorted. With this display arrangement, from zero to four PRIORITY EVENTS
    may be displayed. In the example shown, the Mission/Event Timer called
    "Test Event" has been detected as within 24 hours of Time Zero.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 22


    JPLCLOCK MAIN MENU
    ------------------


                                    Program JPLCLOCK

                  NASA/JPL Multimission Computer Control Center Clock
                                      Version 9401


                       Current time:  20:18:50 PDT   03:18:50 UTC
                       Current date:    06/30/1991     07/01/1991


                    JPLCLOCK will start automatically in 10 seconds



           F1   Program Information            F6   CLOCK Calibration [OFF]
           F2   Set LOCATION CLOCKS            F7   Switch TEXT Mode  [OFF]
           F3   Set EVENT/MISSION TIMERS       F8   Switch PAGE Mode   [ON]
           F4   Set DAYLIGHT and Defaults      F9   DOS Shell (3.3+ ONLY!)
           F5   Read/Save INI & MTD Files     F10   Time Synchronization

        ENTER   Resume Program JPLCLOCK       ESC   Quit Program JPLCLOCK

                Enter selection:

         As with the title screen, JPLCLOCK is awaiting user input; if no
    keyboard input is detected within 10 seconds, the program will
    automatically resume operation. Note that the Main Menu displays the
    current status of CLOCK Calibration, TEXT Mode, and PAGE Mode. Press ENTER
    to immediately resume program operation. Press ESC to quit and return to
    DOS; the program will request that you press ESC a second time to confirm
    that you wish to return to DOS. (To resume JPLCLOCK when this message
    appears, press ENTER.) To go to one of the sub-menus, press the indicated
    Function Key. The purpose and operation of each menu item is described on
    the following pages.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 23


    F1   Program Information
    ------------------------


         Function Key F1 displays a brief description of the program and
    gives the telephone number of my bulletin board system (BBS), RPV ASTRONOMY
    BBS, in Rancho Palos Verdes, California near Los Angeles. This is a free
    access BBS which I maintain as a public service. There are over 1,000 more
    or less regular callers, and the system is frequently busy, so please be
    patient! The BBS computer has a power controller; if the BBS has not
    answered by the fourth ring, hang up and call back in approximately two
    minutes.

         Program JPLCLOCK was written especially for the NASA/JPL Multimission
         Computer Control Center. It provides a main window with local and UTC
         time, four location clocks usually displaying local time at the NASA
         Deep Space Network sites in Goldstone, Canberra, and Madrid, and six
         event timers used to display mission elapsed time or the time for an
         upcoming event of interest. The current version of JPLCLOCK is always
         on my BBS: (310) 541-7299.                                           
                                                                             
         (Press ENTER for more ...)                       David H. Ransom, Jr.

    Pressing the ENTER key will display the following additional HELP
    information:

                  The following special keys are active during the clock display: 
                                                                                   
         ALT-F1   Freeze Display for 5 minutes; Release freeze with any key       
         ALT-F2   Enable/Disable automatic SCREEN BLANKER
         ALT-F5   Select PRIORITY and SELECTED EVENTS (SMALL Main Window ONLY)     
         ALT-F6   Select LARGE or SMALL Main Window                               
         ALT-F7   Enable/Release LAUNCH/HOLD SUPPORT MODE
                  (see documentation for details)
         ALT-F8   Select NORMAL/PAGE/TEXT Mode                                     
                  (See documentation for other active keys.)                       
                  Press ENTER to return to Main Menu                               
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 24


    F2   Set LOCATION CLOCKS
    ------------------------

         JPLCLOCK displays from one to four LOCATION CLOCKS. When the program
    is used in the JPL Mission Control Center, three of the clocks normally
    display the time for the DSN (Deep Space Network) antenna locations; the
    fourth location clock may be used for another location of interest or may
    be left blanked out. The location clocks are numbered #1 through #4 and are
    located in the lower left portion of the display screen below the main
    window in the following relative positions:

              |      Main Window       |  |
              +------------------------+  +---

              +----------+  +----------+  +---
              |    #1    |  |    #3    |  |
              +----------+  +----------+  +---

              +----------+  +----------+  +---
              |    #2    |  |    #4    |  |
              +----------+  +----------+  +---

         Each Location Clock displays the local time at the location using the
    following format (all times in 24-hour notation, HH:MM:SS):

              147   13:24:16 PDT
              --+   -+ -+ -+ --+
                |    |  |  |   |
                |    |  |  |   +---  Time Zone Abbreviation (if present)
                |    |  |  |
                |    |  |  +-------  Local Seconds
                |    |  +----------  Local Minutes
                |    +-------------  Local Hours
                |
                +------------------  Local Day of the Year

         Function Key F2 allows the user to change the name and time zone
    information for the four location clocks displayed below the main window.
    If a location name is PRESENT for a given location clock, that clock will
    be displayed on the screen; if the location name is ERASED (the "Location
    Name" column for the clock is blank in the display), the clock will NOT be
    displayed on the screen. The default location clocks are shown below:

                                                             Uses
                        #  Location Name          UTC Offset  DST
                        -----------------------------------------
                        1  GDS  Goldstone              -8.00  YES
                        2  JSC  Houston                -6.00  YES
                        3  CAN  Canberra               11.00   NO
                        4  MAD  Madrid                  1.00   NO

                        Enter LOCATION # to change:

    JPLCLOCK will automatically resume operation if no keyboard input is
    detected within 30 seconds. Each keystroke resets the 30 second timer.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 25


    Press ENTER to cancel this function and return to the Main Menu making no
    changes. To continue, enter the number of the location clock to change and
    press ENTER. Then enter the new location name for that clock:

                        Enter new LOCATION NAME:

    Press the TAB key to leave the name unchanged for this clock and skip to
    the time information. Press ENTER to erase the name and remove the clock
    from the display screen. To enter a new or corrected location name, type
    the new name and then press ENTER. JPLCLOCK will automatically capitalize
    the first letter of each word if it is lower case.
         In order to show the local time correctly for each location, JPLCLOCK
    must know the UTC Offset for the location; this is the number of hours
    which must be ADDED to UTC (Universal Coordinated Time) in order to obtain
    the local STANDARD time for the location. Do NOT include the additional
    hour if the location is on U.S. Daylight Savings Time; DO include the
    additional hour if the location is on daylight or summer time but the time
    changes do not correspond to those used in the United States. See the
    additional discussion below.

                        Enter New UTC Offset (hours):

    Press the TAB key to leave the current UTC Offset value unchanged. Press
    the ESC key to cancel all changes to this location clock. Otherwise, type
    the new UTC Offset in hours (and decimal parts of an hour if necessary) and
    then press ENTER.
         JPLCLOCK will independently adjust each location clock time for U.S.
    Daylight Savings Time if the special flag in the column "Uses DST" is
    marked "YES". As a general rule, therefore, respond "YES" if the location
    is within the United States (including Alaska and Hawaii); respond "NO" if
    the location is outside the United States.

                        Uses US Daylight (N=NO, Y=YES):

         IMPORTANT NOTE: When the main Daylight Flag is changed (using F4+F3
    from the Main Menu), the appropriate correction will be automatically made
    for all locations which indicate "YES" in the "Uses DST" column. Locations
    outside the United States which use daylight or summer time but which
    change at different times from the United States should indicate "NO" in
    the "Uses DST" column and must be manually adjusted for each time change.
         
         When all of these questions have been answered, the information will
    be updated on the screen and the user may either continue to another
    location clock or return to the Main Menu.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 26


    F3   Set EVENT/MISSION TIMERS
    -----------------------------

         One of the most important functions of JPLCLOCK is to be able to
    display Mission Elapsed Time (MET) or Countdown/Countup Time for a variety
    of missions and events. MIssion Elapsed Time usually measures the time
    since the mission was launched and is the primary time measure used for the
    Mission Timeline, the schedule of planned events and operations; this
    applies equally to short duration missions such as the Space Shuttle as
    well as to long duration missions such as Voyager and Hubble Space
    Telescope. Countdown/Countup Times may be critical events in the progress
    of a mission, such as scheduled Launch Time or Venus Orbit Insertion for
    Magellan, and controllers need to be able to judge the time remaining until
    (or time passed since) specific tasks or operations are to be (or were
    supposed to have been) performed.
         JPLCLOCK is able to independently time up to 60 different events or
    missions using six MISSION TIMER WINDOWS on the display screen and
    switching from one mission timer "page" to another to display up to ten
    pages. The mission timer windows are numbered #1 through #6 and are located
    on the right of the display screen beside the main window in the following
    relative positions:

              ---+  +----------------+
                 |  |    TIMER #1    |
               M |  +----------------+
               a |
               i |  +----------------+
               n |  |    TIMER #2    |
                 |  +----------------+
               W |
               i |  +----------------+
               n |  |    TIMER #3    |
               d |  +----------------+
               o |
               w |  +----------------+
                 |  |    TIMER #4    |
              ---+  +----------------+

              ---+  +----------------+
                 |  |    TIMER #5    |
              ---+  +----------------+

              ---+  +----------------+
                 |  |    TIMER #6    |
              ---+  +----------------+

         Each Mission/Event Timer displays the current time value for that
    mission or event using one of the following formats (all times are shown as
    HH:MM:SS, hours:minutes:seconds):

              143  13:01:47       The event occurred 143 days plus time ago.
                                  When applied to a mission, this format is
                                  measured from the time of launch and is known
                                  as Mission Elapsed Time (MET) and is used for
                                  all mission event planning.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 27



              -16  01:33:19       The event will occur in 16 days plus time.

               -0  07:44:51 *     The event will occur in the time shown and a
                                  flashing asterisk denotes less than 24 hours.

               -0  00:58:29 **    The event will occur in the time shown and
                                  two flashing asterisks denote less than 1
                                  hour remains.

               -0  00:08:14 ***   The event will occur in the time shown and
                                  three flashing asterisks denote less than 10
                                  minutes remain.


         Pressing F3 from the Main Menu displays the menu for setting the
    MISSION/EVENT TIMERS and the SELECTED EVENTS:

                            F1   Set   MISSION/EVENT TIMERS       
                            F2   Clear MISSION/EVENT TIMERS       
                            F3   Set   SELECTED EVENTS           
                            F4   ON    MISSION/EVENT TIMER NUMBERS

                         ENTER   Return to Main Menu

    Press the Function Key for the desired selection or press ENTER to return
    to the Main Menu.

    Set MISSION/EVENT TIMERS
    ------------------------

         Using F1, each Mission/Event Timer may be set to any desired time and
    date in the past or future over a range of from approximately minus 27
    years (-9,999 days before the event) to approximately plus 274 years
    (99,999 days after the event) referenced to the current time. Given the
    time scale of interplanetary missions such as Voyager 1 and 2 or Pioneer
    11, these time ranges are reasonable and necessary even though it may seem
    like "overkill" for a 5-day Space Shuttle mission. The Mission Timer Window
    background color (for color monitors) is RED if the event has not yet
    occurred and GREEN if the event has occurred. The color switch occurs when
    the Mission Timer reaches 0 days and 00:00:00 (hours:minutes:seconds).
         As a special feature to call attention to events about to occur, a
    single asterisk ("*") appears to the right of the countdown time when the
    event is less than 24 hours from occurrence; this changes to two asterisks
    at T minus one hour and to three asterisks at T minus ten minutes. The
    asterisks are removed once the scheduled event time occurs.
         When JPLCLOCK is operated in the NORMAL mode, Mission Timers #1
    through #6 are displayed continuously; the remaining 54 timers are neither
    checked nor displayed. However, when JPLCLOCK is operated in the PAGE mode,
    all 60 Mission Timers are checked and are displayed if a valid time and
    date has been entered. The Mission Timers are divided into ten pages of six
    timers each. The pages are numbered 0 through 9; Mission Timers #1 through
    #6 appear on Page 0, Mission Timers #7 through #12 appear on Page 1, and so
    forth. If any one of the timers in a given page is valid, that page will be
    displayed; if no timers in a given page are valid, that page will be
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 28


    skipped. Each page is displayed for 30 seconds and then the program cycles
    to the next valid page. With active Mission Timers in each of the ten
    pages, it can require up to 5 minutes to complete a full cycle through the
    timers.
         When the PAGE mode is active and JPLCLOCK is cycling through all
    active Mission Timers, a special "bar meter" is displayed at the top right
    of the Mission Timers. This is a row of ten special square symbols, one for
    each of the ten Mission Timer pages, which indicates the status of the
    page. If there are no active Mission Timers on the page, the symbol is
    GRAY. If one or more Mission Timers on the page is in the countdown mode
    (the event has not yet occurred), the symbol is RED. If all active Mission
    Timers on the page are in the countup or Mission Elapsed Time mode, the
    symbol is GREEN. The current active page is flashing.
         With up to 60 Mission Timers active in the PAGE mode, it might be easy
    to overlook an event which is scheduled to occur in the near future. The
    flashing asterisks described above may help to avoid this situation but
    JPLCLOCK solves the problem by holding the display on a page if any Mission
    Timer on that page will reach Time Zero within the next hour. When the
    current page is being held in this manner, the word "HOLD" appears above
    the Mission/Event Timers and the flashing symbol corresponding to the held
    page changes to YELLOW. The HOLD remains in effect until all timers on that
    page are either more than one hour before Time Zero or have passed Time
    Zero by more than one hour OR until another page includes events closer to
    their Time Zero. When the hold is removed, normal cycling is resumed and
    the program checks for other potential HOLD opportunities on each page
    before selecting the next page to display. See also the discussion below
    (in the section Set DAYLIGHT and Defaults) regarding setting the PAGE Delay
    for additional suggestions.
         Not all Mission Timers on a particular page must be programmed. If the
    Event/Mission Name is blank, that Mission Timer will not be displayed and
    its position on the display screen will be blank. The user may therefore
    arrange both which page(s) will be displayed as well as what position(s)
    is(are) used to display the active timers on a given page. As noted above,
    if ALL Mission Timers on a particular page are blank, that page will be
    skipped.
         Function Key F3 provides the capabilities to enter, erase, or correct
    the Mission Timers. The first time F3 is used, Page 0 and the first six
    Mission Timers will be displayed; subsequent uses of F3 may start on a
    different page. The Page Number is shown along with the data for the
    individual Mission Timers on that page.


             #  Event/Mission Name      Time(UT)  Date (MDY)  Julian Date
    PAGE     ---------------------------------------------------------------
             1  Galileo                 11:00:00  01/22/1990  2447913.958333
    +---+    2  Magellan                08:00:00  05/09/1989  2447655.833333
    |   |    3  Ulysses                 17:46:00  10/06/1990  2448171.240278
    |   |    4  Hubble Space Telescope  12:33:52  05/07/1990  2448019.023519
    |   |    5  Gamma Ray Observatory   15:22:45  04/05/1991  2448352.140799
    +---+    6  ROSAT Observatory       21:47:59  06/01/1990  2448044.408322
             (Home, PgUp, PgDn, ENTER to return to Main Menu)
             Enter EVENT # to change (1-60):

         The reminder enclosed in parentheses indicates the special keys that
    are active at this prompt:
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 29



              Home      Display PAGE 0
              PgUp      Go to NEXT PAGE
              PgDn      Go to PRIOR PAGE
              ENTER     Return to Main Menu

    Use PgUp or PgDn to review each of the ten Mission Timer pages or type the
    number of the desired Mission Timer followed by ENTER to edit that Mission
    Timer. When a Mission Timer has been selected, a flashing diamond will
    appear to the left of the Mission Timer number in the display and you will
    be asked to enter a new MISSION NAME. For the following example, Mission
    Timer #7 was desired and "7" was typed:

             #  Event/Mission Name      Time(UT)  Date (MDY)  Julian Date   
    PAGE     ---------------------------------------------------------------
           * 7  Voyager 1               12:58:00  09/05/1977  2443392.040278
    -+      8  Voyager 2               14:24:00  08/20/1977  2443376.100000
      |      9                                                             
      |      10                                                             
      |      11                                                             
    --+--    12                                                             
             (TAB to SKIP, #nn to COPY, ESC to CANCEL, ENTER to ERASE #7 data)
             Enter #7 EVENT/MISSION NAME:                                   

         The asterisk shown above will actually be displayed as a flashing
    diamond to indicate the selected Mission Timer. The reminder enclosed in
    parentheses indicates the special keys that are active at this prompt:

              TAB       SKIP the name, leaving it unchanged, and continue.
              ESC       CANCEL making changes to this Mission Timer
              ENTER     ERASE all data for this Mission Timer

         In some cases, you may wish to copy an event from one Mission Timer to
    another. If the event is simply being moved, you would then go back and
    erase the original entry; otherwise, the event will appear in multiple
    Mission Timers (which might be desired for certain important events). The
    "#nn" format may be used for this purpose by substituting the SOURCE
    MISSION TIMER NUMBER for "nn". Thus, after selecting the DESTINATION
    MISSION TIMER NUMBER in the previous step, you would enter "C13" to copy
    all data from Mission Timer #13 to the selected Mission Timer.
         In other cases, you may wish to prepare a group of related Mission
    Timers relative to a single time. A sequence of operations following launch
    or satellite deploy are examples of this situation. To do this, first
    select the "base time" event and enter its information into a selected
    Mission Timer. Next, select each successive Mission Timer whose time is
    relative to the "base time" and use one of the following formats:

              #nn+ddd/hh:mm:ss
              #nn+hh:mm:ss
              #nn-ddd/hh:mm:ss
              #nn-hh:mm:ss

    where:

              #    Specifies the COPY syntax
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 30


              nn   SOURCE MISSION TIMER NUMBER, 1 to 60
              +    Specifies ADD to "base time"
              -    Specifies SUBTRACT from "base time"
              ddd  The number of DAYS to add/subtract to "base time"
              /    Separates DAYS from TIME
              hh   The number of HOURS to add/subtract to "base time"
              mm   The number of MINUTES to add/subtract to "base time"
              ss   The number of SECONDS to add/subtract to "base time"
              :    Separates hours:minutes and minutes:seconds

    Note that the days portion of the command, "ddd/", may be omitted if the
    value is zero; omitting the days is equivalent to a days portion of "000/".
    The number of digits shown for each portion of the command may not be
    exceeded, but leading zeroes may be omitted. The comma (",") may be used in
    place of the colon (":"). Times may differ by as little as one second. (In
    fact, they may be identical if you wish.)
         After the information is copied to the new Mission Timer, the program
    requests a new Mission/Event Name:

              (TAB to SKIP, ENTER to ERASE #7 data)
              Enter #7 NEW MISSION/EVENT NAME:

    Enter the new name or press TAB to leave the name unchanged, ENTER to erase
    the new data.
         As an example of relative Mission Timer programming, suppose that the
    "base time" for a sequence of events is on 7/11/1991 at 13:44:00 UTC and
    that a series of subsequent events will occur at this "base time" plus 37
    seconds, 1 minute and 30 seconds, and 3 hours and 7 minutes. The following
    commands will set up this sequence of Mission Timers:

              25             Event Timer Number
              Base Event     Event Name
              7/11/91        Event Date
              13:44          Event Time

              26             First Subsequent Timer Number
              #25+00:00:37   Relative time to Mission Timer 25

              27             Second Subsequent Timer Number
              #25+00:01:30   Relative time to Mission Timer 25

              28             Third Subsequent Timer Number
              #25+03:00:07   Relative time to Mission Timer 25

    After these commands have been entered, Mission Timers 25 through 28 will
    contain the base event and the three subsequent events. Since the "copy"
    format has been used for the subsequent events, the names will be identical
    in all four Mission Timers. You may then edit Mission Timers 26 through 28
    by selecting them in turn, entering a new event name, then pressing TAB in
    place of a date entry to leave that information unchanged.
         Future events are sometimes rescheduled. To accommodate this
    situation, the "#nn" command may be used to copy an event to the same
    Mission Timer with a positive or negative time adjustment. Select the
    Mission Timer number you wish to adjust, enter the "#nn" command as
    described above (including the relative time adjustment) and the change
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 31


    will be made. For example, to advance the time for Mission Timer 44 by one
    hour and thirty minutes, enter the following commands:

              44             Timer Number to adjust
              #44+1:30       Advance the time by 1:30

    This example illustrates a "shortcut": if the seconds are zero, they may be
    omitted. Similarly, if both minutes and seconds are zero, both may be
    omitted. The hours could also have been entered with a decimal fraction and
    the minutes omitted: "#44+1.5" to achieve the same result. The optional
    days ("#44+3/1:30" to advance the time by 3 days, 1 hour, 30 minutes) could
    have been used if required.
         If you wish to enter new data for the selected mission timer, type the
    new name for this Mission Timer followed by ENTER. You will then be asked
    to enter the new DATE for this timer:

              (ESC to CANCEL)               
              Enter new DATE (MM/DD/YYYY or JD/MJD):

    Press ESC to CANCEL making changes to this Mission Timer or type the new
    DATE followed by ENTER. Dates are normally entered using "MM/DD/YYYY"
    format where "MM" is the MONTH (month number), "DD" is the DAY, and "YYYY"
    is the YEAR. JPLCLOCK will also accept a two-digit year and add 1900 to the
    value entered; "1991" and "91" will both be accepted as "1991". JPLCLOCK
    will also accept several "JD" (Julian Date) formats by prefixing the date
    entry with one of the following:

           Prefix        Julian Date   Format Name               Starting Date
           -------------------------------------------------------------------
               JD     2448424.375000   Standard Julian Date   (-4713 JAN  1.5)
              MJD       48423.875000   Modified Julian Date    (1858 NOV 17.0)
              DJD       33404.375000   Dublin Julian Date      (1900 JAN  0.5)
              TJD        8423.875000   Truncated Julian Date   (1968 MAY 23.0)

    All of the Julian Date formats in the example are equal to June 16, 1991,
    at 14:00 PDT. "JD" is the standard format used by astronomers and most
    scientists. The other formats have been developed to reduce the number of
    digits required to uniquely identify a specific date but have more
    restricted range if negative numbers or large numbers are to be avoided.
    NASA, for example, frequently uses the "TJD" format.

    NOTE: When one of the Julian Date formats is used, the time is implicit and
    the "New TIME" prompt will be skipped. Thus, an entry of "JD2448424.375" or
    "TJD8423.875" would yield the same time and date as "6/16/91" (for DATE)
    and "14:00P" (for TIME).

         After the new date has been entered (and provided you did not use one
    of the Julian Data formats), you will be prompted for the new TIME:

              (ESC to CANCEL)
              Enter new TIME (UTC or Zone):

    Type the desired new time using the "HH:MM:SS" format followed by ENTER.
    JPLCLOCK is very flexible as to the time format. JPLCLOCK requires the 24-
    hour format. Decimal fractions for the last value entered are accepted,
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 32


    leading zeroes are NOT required, the separator may be either the colon
    (":") or the comma (","), and the entry may omit values which are zero.
    Each of the following examples will be accepted as 14:15 (2:15 PM):

              14:15:00
              14,15
              14.25

    JPLCLOCK assumes that the time entered is Coordinated Universal Time (UTC)
    unless a suffix is added to indicate otherwise. The following time zone
    suffixes are supported by JPLCLOCK:

              U    UTC       Universal Coordinated Time
              A    AST/ADT   Atlantic Time Zone
              E    EST/EDT   Eastern Time Zone
              C    CST/CDT   Central Time Zone
              M    MST/MDT   Mountain Time Zone
              P    PST/PDT   Pacific Time Zone
              Y    YST/YDT   Yukon Time Zone (sometimes "Alaska")
              H    HST/HDT   Hawaiian Time Zone

         Except for UTC, JPLCLOCK will automatically adjust the entered time
    for the appropriate time zone AND for daylight savings time (if in effect).
    Thus, an entry of "14:00P" will be interpreted as Pacific Standard Time
    (PST) if the Daylight Flag is OFF, and as Pacific Daylight Time (PDT) if
    the Daylight Flag is ON. If no suffix is included or if the "U" suffix is
    added, no adjustment for the Daylight Flag will be made and the time entry
    will be accepted as UTC. By using the appropriate time zone suffix, times
    may thus be entered directly in local time for each time zone in the United
    States, Alaska, and Hawaii without making any conversions (or mistakes!).
    JPLCLOCK makes the required conversions to the time (and date, if
    necessary) and displays the resulting Mission Timer values in UTC.

    Clear MISSION/EVENT TIMERS
    --------------------------

         As the function name suggests, this clears all Mission/Event Timers.
    While this process could be accomplished without a separate function key,
    it was rather time consuming. Several users suggested a "master clear" and
    it has been implemented. All Mission/Event Timers are cleared and reset.

    Set SELECTED EVENTS
    -------------------

         Press F2 to set the SELECTED EVENTS. The program will display the
    currently selected SELECTED EVENTS, if any, and remind you that the
    SELECTED EVENTS are displayed ONLY when the SMALL Main Clock window is
    active. To make the SMALL Main Clock window active, press ALT-F6 when the
    Main Clock window is on the screen.

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 33


                SELECTED EVENTS are active with SMALL Main Window ONLY!

                        #    MT#    Mission/Event Name
                        ----------------------------------------
                        1    11     Hubble Space Telescope
                        2    17     Gamma Ray Observatory
                        3    23     Voyager 1
                        4    24     Voyager 2

                  (ENTER to CLEAR, TAB to SKIP, ESC to CANCEL)
                  Enter MISSION/EVENT TIMER # for Selected Event #1:

    In the sample display above, the column marked "#" lists the four SELECTED
    EVENT timers in order; the column marked "MT#" lists the Mission/Event
    Timer which is associated with the corresponding SELECTED EVENT; and, the
    column marked "Mission/Event Name" lists the name of the selected
    Mission/Event Timer.
         The information for each SELECTED EVENT is requested in turn. The
    first prompt asks for Selected Event #1. As noted, press ENTER to clear
    that event, press TAB to skip to the next event, or press ESC to cancel and
    return to the Main Menu.
         The only information that can be entered here is the Mission/Event
    Timer number which you wish to be associated with each SELECTED EVENT. The
    actual data, the event name, date, and time, must already have been entered
    into the Mission/Event Timer (F3+F1 from the Main Menu). Note also that the
    while the full Mission/Event Name is displayed on the menu as shown above,
    the actual window on the screen will truncate the name to a maximum of 19
    characters; this is because the SELECTED EVENT windows are somewhat
    narrower than the main Mission/Event Timer windows. If you wish to edit the
    name so that it will fit correctly in the SELECTED EVENT windows, you must
    edit the Mission/Event Timer entry using F3+F1 from the Main Menu (or just
    F1 from the event menu).

    MISSION/EVENT TIMER NUMBERS
    ----------------------------

         The Mission/Event Timer Windows may be configured to display the
    window number (1 to 60) or not. If the window number will NOT be displayed,
    the F4 menu item will include the word "OFF"; if the window number WILL be
    displayed, the F4 menu item will include the word "ON". The window number
    is displayed at the bottom left of the window border, as illustrated in the
    following example where the Hubble Space Telescope is assigned
    Mission/Event Timer #11:

              +[Hubble Space Telescope]--+
              |        654   15:58:23    |
              +[11]----------------------+

         In cases where the same window position is assigned to the same
    mission or event (as, for example, by assigning the top window always to
    the Hubble Space Telescope for all pages), the first assigned timer number
    will be displayed for all occurences in sequence.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 34


    F4   Set DAYLIGHT and Defaults
    ------------------------------

         Function Key F4 allows you to switch the system from local STANDARD
    time to local DAYLIGHT time and set a number of program defaults. Pressing
    F4 from the Main Menu displays the following menu:


             Enter selection:
                               F1   Switch STANDARD/DAYLIGHT Time
                               F2   Set LOCAL NAME and TIME ZONE
                               F3   Restore Program DEFAULT DATA
                               F4   Set PAGE and TEXT Mode Delays [15,30]
                               F5   Enable/Disable SCREEN BLANKER [ON]
                              ESC   Return to Main Menu
                            ENTER   Resume Program JPLCLOCK

                                    Enter selection:

         Pressing ESC will return you to the Main Menu.

         Pressing ENTER will resume operation of program JPLCLOCK.

         Pressing F1 will switch the Daylight Flag between Standard time and
    Daylight time. NOTE: This function does NOT change your computer's clock;
    you must set the correct local time BEFORE using this function!

         Pressing F2 will allow you to enter a new name for your location and
    to set its standard UTC Offset (in hours) and Daylight Flag.

         Pressing F3 will restore the "hard-coded" program default data for the
    Local Name, Location Clocks and Mission Timers.

         Pressing F4 will prompt you to enter new values for the PAGE delay and
    the TEXT delay. See further discussion which follows below.

         Pressing F5 will toggle the SCREEN BLANKER between ON and OFF and the
    prompt on the menu will change accordingly. When the SCREEN BLANKER is OFF,
    the screen is always active when the clocks are displayed. When the SCREEN
    BLANKER is ON, the screen will be cleared if five minutes passes without a
    key being pressed on the keyboard. The screen will be immediately restored
    if any key (except non-typing keys such as CTRL and SHIFT) is pressed; the
    screen is also automatically restored at 29 and 59 minutes past the hour.

    Set PAGE and TEXT Mode Delays
    -----------------------------

         As noted above, pressing F4 on this menu will allow you to set the
    PAGE and TEXT Mode Delays. The current values are shown at the right of the
    prompt. The following information will be displayed and you will be asked
    for the PAGE Delay:

              PAGE Delay sets the time to display each page of Mission
              Timers. TEXT delay set the time to display each text page.

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 35


              PAGE Delay must be between 5 and 900 seconds.
              TEXT Delay must be between 5 and 900 seconds AND an even
              multiple of PAGE Delay. The times are adjusted if necessary.

              Enter PAGE Delay [15] (seconds):

    The current PAGE Delay is shown in square brackets. Enter the desired new
    value for the PAGE Delay in seconds or press ENTER to leave the present
    value unchanged. You will then be asked for the TEXT Delay:

              Enter TEXT Delay [30] (seconds):

    The current TEXT Delay is shown in square brackets. Enter the desired new
    value for the TEXT Delay in seconds or press ENTER to leave the present
    value unchanged.
         Note the minimum and maximum values allowed for these delays, 5 and
    900 seconds respectively. Note also that the TEXT Delay must be an even
    multiple of the PAGE Delay (for internal programming reasons). If this is
    not the case, TEXT Delay will be automatically adjusted accordingly. The
    values shown in the examples above are recommended as the minimum values
    for JPLCLOCK. Smaller values may allow insufficient time for reading.
         JPLCLOCK was originally designed for use with multiple events which
    are well spaced in time such as NASA planetary missions. Typical events in
    this environment are usually spaced minutes, hours, or even days apart.
    When the Mission/Event Timers are used for fast paced events such as the
    launch of a space shuttle (where events are separated by as little as a
    second or two), set the PAGE Delay to 5 seconds and disable the TEXT mode.
    Using that technique, JPLCLOCK will check all timers every five seconds and
    select the page with events closest to Time Zero.
         However, even with the PAGE Delay set to 5 seconds JPLCLOCK may miss
    certain events which are spaced only a few seconds apart and which are on
    different Mission/Event Timer pages. This is dependent upon the actual
    times programmed compared to the PAGE Delay time; if an event occurs just
    after the PAGE Delay, that page will be held for the full delay time and
    other pages will not be checked until after the expiration of the delay
    time. With the PAGE Delay set to 5 seconds, this means that page switching
    may not occur until as many as four seconds have passed since Time Zero for
    an event on a given page. Where practical, events should be programmed such
    that there is more than twice the PAGE Delay separating events on different
    pages.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 36


    F5   Read or Save INI and MTD Files
    -----------------------------------

         Two types of files are used to save and restore information by
    JPLCLOCK, distinguished by the filetypes ".INI" and ".MTD". INI files
    include all program initialization, Location Clock, and Mission/Event Timer
    data. MTD files include data for from 1 to 60 Mission/Event Timers only.
         Pressing Function Key F5 from the Main Menu will display the following
    menu:

              F1   Read external INI File      F3   Read external MTD File
              F2   Save external INI File      F4   Save external MTD File
             ESC   Return to Main Menu
           ENTER   Resume Program JPLCLOCK

                   Enter selection:

         JPLCLOCK reads the file JPLCLOCK.INI each time it is started, and
    writes a new JPLCLOCK.INI file each time the program is halted. This INI
    file contains all the information about the local installation, the
    Location Clocks, and the Mission Timers. For installations where only the
    first six Mission Timers are used, this information will change only
    infrequently and additional INI files will probably not be required.
         Users may find it convenient to re-read the normal INI file,
    JPLCLOCK.INI, if they have incorrectly changed information and wish to
    restore the original information. (NOTE: Exiting program JPLCLOCK in this
    situation will cause the incorrect information to be written to file
    JPLCLOCK.INI and the original data in that file will be permanently lost!)
    As a protection against this sort of problem, it is recommended that all
    users create a standard INI file, named STANDARD.INI for example, that
    represents the normal program configuration. This is most easily done by
    verifying the configuration of JPLCLOCK (by running the program) and then
    quiting the program and copying file JPLCLOCK.INI to file STANDARD.INI.
    Function Key F1 may then be used from this menu to reload the standard
    configuration at any time.
         However, installations using JPLCLOCK in the PAGE mode may find that
    advance preparation of INI and MTD files (using another computer running
    JPLCLOCK) is very helpful in preparing for upcoming events on multiple
    missions. In order to facilitate this process, JPLCLOCK can both read and
    write INI files. This takes advantage of JPLCLOCK's internal editing
    capabilities (using Function Key F3 from the Main Menu) and may avoid
    errors due to manual editing and time/date conversions, especially when
    various different time zones are involved. In most cases, only the
    Mission/Event Timers change and therefore the MTD file format is
    recommended. When a completely new setup is configured, the INI file format
    is recommended.
         A new set of Mission/Event Timers can be prepared on an "offline
    computer", tested, and written to an MTD file for use on an "online
    computer". Files may be exchanged via disk, local area networks, or
    telecommunications software. Since the dates and times in an MTD file are
    saved in the Julian Date format, these date are independent of time zone
    and location. Once the new MTD or INI file has been loaded onto the "online
    computer", JPLCLOCK may be paused, the new file read, and program operation
    resumed. Performed in this manner, the entire updating process will take
    the "online computer" offline for a few seconds. Any number of INI and MTD
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 37


    files may be prepared in this fashion, the only requirement being that they
    have unique names and the correct filetype.


    READ and SAVE INI Files
    -----------------------

         INI files MUST have the file type ".INI". The filename may be any
    legal file name EXCEPT "JPLCLOCK.INI". Manual editing of INI files is NOT
    recommended; however, if this is done be certain to use a simple ASCII
    editor or an editor which has a "non-document" mode. Although the format of
    the INI file uses a simple comma-delimited format, an error in the file
    structure may cause the program to operate incorrectly or to crash (halt
    with an error message). If all else fails, delete the file JPLCLOCK.INI and
    restart the program; JPLCLOCK will then use its internal default data and
    construct a new INI file.
         Press F1 to read an INI file or F2 to write an INI file. All files are
    assumed to be in the current drive and directory. For file read operations,
    the file must exist. For file write operations, if the file does not exist
    it will be created and if the file does exist it will be overwritten. If
    either F1 or F2 is pressed, the following prompt will be displayed:

         INI files contain the setup and mission/clock data for JPLCLOCK.
         Enter the name of the INI file which you wish to READ or SAVE.
         Do NOT include a filetype; the program automatically adds '.INI'.
         (ENTER = 'JPLCLOCK', ESC to CANCEL)
         Enter filename to READ (without .INI):

    If you have pressed F2 to SAVE, the word "READ" will be replaced by the
    word "SAVE" in the sample above. Press ESC to CANCEL the file read or
    write. Press ENTER to use the default file name JPLCLOCK.INI. Otherwise,
    type the filename WITHOUT the ".INI" filetype followed by ENTER. JPLCLOCK
    will automatically append ".INI" to the filename and then read or write the
    file and return to this menu.


    READ and SAVE MTD Files
    -----------------------

         MTD files are processed in a manner almost identical to INI files. The
    default filename used if ENTER is pressed is JPLCLOCK.MTD. The principal
    difference is that since only the Mission/Event Timer data is included,
    JPLCLOCK must know which timers to SAVE or the first timer to which data
    should be READ.
         Pressing F3 to READ an MTD file will display the following prompts in
    turn:

         Enter FIRST TIMER NUMBER [1]:
         Enter TIME OFFSET
  • :

    In each case, the number enclosed in square brackets "[...]" is the default
    response if ENTER is pressed. When reading an MTD file, only the first
    Mission/Event Timer number is required. JPLCLOCK will read the file until
    all data have been read or until timer 60 has been read, whichever comes
    first. You may also add a TIME OFFSET to the Mission/Event Timer data as it
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 38


    is read; this may be helpful if the schedule for the events in the MTD file
    has changed. The TIME OFFSET is entered in one of the following formats:

              +ddd/hh:mm:ss
              +hh:mm:ss
              -ddd/hh:mm:ss
              -hh:mm:ss

    where:

              +    ADD the TIME OFFSET to event time
              -    SUBTRACT the TIME OFFSET from event time

              ddd  The number of DAYS to add/subtract to event time
              /    Separates DAYS from TIME
              hh   The number of HOURS to add/subtract to event time
              mm   The number of MINUTES to add/subtract to event time
              ss   The number of SECONDS to add/subtract to event time
              :    Separates hours:minutes and minutes:seconds

    Note that the days portion of the command, "ddd/", may be omitted if the
    value is zero; omitting the days is equivalent to a days portion of "000/".
    The number of digits shown for each portion of the command may not be
    exceeded, but leading zeroes may be omitted.
         Pressing F4 to SAVE an MTD file will display the following prompts in
    turn:

         Enter FIRST TIMER NUMBER [1]:
         Enter LAST TIMER NUMBER [60]:

    In each case, the number enclosed in square brackets "[...]" is the default
    response if ENTER is pressed. The only constraints are that the LAST TIMER
    NUMBER must be greater than or equal to the FIRST TIMER NUMBER, and no
    timer number may exceed 60. After these special prompts are answered, the
    next prompt requests the MTD filename:

         MTD files contain only selected MISSION TIMER data for JPLCLOCK.
         Enter the name of the MTD file which you wish to READ or SAVE.
         Do NOT include a filetype; the program automatically adds '.MTD'.
         (ENTER = 'JPLCLOCK', ESC to CANCEL)
         Enter filename to READ (without .MTD):

    If you have pressed F4 to SAVE, the word "READ" will be replaced by the
    word "SAVE" in the sample above. Press ESC to CANCEL the file read or
    write. Press ENTER to use the default file name JPLCLOCK.MTD. Otherwise,
    type the filename WITHOUT the ".MTD" filetype followed by ENTER. JPLCLOCK
    will automatically append ".MTD" to the filename and then read or write the
    file and return to this menu.
         The MTD file format is ideal for preparing Mission/Event Timer data
    for multiple systems whose configuration and/or time zone may not be the
    same. Since the time and data information is saved in the Julian Date
    format, it is independent of the local time zone for any particular
    installation of JPLCLOCK. Further, since the Mission/Event Timer number is
    specified by the ultimate user, different users may select different timer
    numbers to suit their own installations.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 39


         Included with the JPLCLOCK files is STS43.MTD; this file has 13 events
    associated with Space Shuttle Mission STS-43, scheduled for July 23, 1991.
    The events include the important milestones of the ascent phase, the deploy
    events for TDRS-E, and the deorbit burn and landing. Although the flight of
    STS-43 is a one-time event, the MTD file may serve as an example of how to
    prepare and use MTD files; for example, read the file into the system
    starting at timer #43.
         As with file STS43.MTD, events of interest may be prepared in advance
    and distributed to users without regard for their location or time zone. By
    maintaining a backup copy of their "standard" INI file, users may freely
    read in MTD files, use them for as long as desired, then restore their
    original configuration by reading in their "standard" INI file.
         The same techniques may be used to move events from one set of timers
    to another. First write the MTD file for the desired events, then clear the
    timers involved (either one by one using F3+F1, or by reading in your
    "standard" INI file), then read the MTD file just created using the new
    timer numbers. After some experimentation, I discovered that it would be
    handy to be able to add a time offset (plus or minus) to events as they are
    being read from the MTD file so that schedule changes or delays might be
    easily accommodated; the next version of JPLCLOCK will include an
    additional prompt to permit you to add such an offset which will be applied
    equally to all timer events being read.
         Another use for the MTD file is to easily set up all active
    Mission/Event Timer pages with the same set of events for the first several
    timers. The sample INI file distributed with JPLCLOCK illustrates this
    technique; the first three timers are always the same and only the bottom
    three change from page to page. In this case, save an MTD file with the
    desired "constant" events, then read that MTD file back on each active
    timer page at the appropriate timer number. The "constant" events could as
    easily be the last timers on each page by selecting the appropriate timer
    numbers.


    INI Files from Other Locations
    ------------------------------

         Except when JPLCLOCK is first started, the information specific to
    your location (Location Name, UTC Offset, Daylight Flag, etc.) is NOT
    processed when you read an INI file using F1. Therefore, if you receive an
    INI file from elsewhere, you should rename it to a convenient name (which
    might remind you of the source of the data, for example) and then read it
    into JPLCLOCK using F3. Since all of the remaining information in the INI
    file is recorded using UTC, JPLCLOCK will be able to make the necessary
    time conversions for display in your time zone.
         If you wish to use missions or events from a received INI file, you
    may read it in using F5, then save the desired information in selected
    Mission Timer Pages to an MTD file. Having saved the information, you may
    then re-read your own JPLCLOCK.INI file (press ENTER when asked for the INI
    filename) and read the mission or event data you saved to the MTD file
    using F5 as usual. Note that the times and dates shown on each Mission
    Timer page are always Coordinated Universal Time (UTC), not your local
    time, so the times will automatically be adjusted for your location and
    time zone.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 40


    F6   Self-Calibration using TIMESET
    -----------------------------------

                               ********************
                               *  IMPORTANT NOTE  *
                               ********************

              Calibration of the hardware and software clocks may also be
         performed when program RIGHTIME is installed. In that case,
         RIGHTIME calculates its own adjustments and JPLCLOCK's internal
         adjustments are disabled. RIGHTIME is recommended for precision
         timekeeping. See the documentation for RIGHTIME for details.

                                     * * * * *

         Function Key F6 enables a special self-calibration procedure which
    causes JPLCLOCK to use program TIMESET to perform a series of calibration
    measurements over a period of 7 hours. Note that TIMESET must have been
    correctly configured and tested prior to automatic use. See the procedure
    for configuring TIMESET in the section F10 TIME SYNCHRONIZATION below and
    read the TIMESET documentation.
         When the Self-Calibration procedure is initiated, JPLCLOCK immediately
    makes a call using TIMESET and resets the drift and offset parameters. The
    program then makes subsequent calls at 1, 2, and 4 hour intervals (for a
    total of four calls) to enable calculation of new parameters. When the last
    call has been completed, a reasonable calibration of the DOS clock should
    have been calculated.
         The computer must be allowed to run JPLCLOCK continuously during the
    procedure. However, the usual commands are available for use between calls
    PROVIDED you do not exit to DOS and the clocks are displayed when the time
    comes to make each call. Of particular interest after the second call (in
    other words, after more than one hour has elapsed since the procedure was
    started) is the calculated DOS Clock Drift. With the main clock display on
    the screen, press ENTER twice to obtain the Main Menu, then press F10+F1 to
    view the current data:

                           DOS time:  06:45:26.17      07-05-1991
                          CMOS time:  06:45:27         07-05-1991
                      JPLCLOCK time:  06:45:27 PDT   13:45:27 UTC
                      JPLCLOCK date:    07/05/1991     07/05/1991

                    JPLCLOCK will start automatically in 88 seconds

                     Current Julian Date:   2448443.073229
                     Last Synchronized:     2448442.500926
                     Time since Last Sync:        0.572303 days
                     Current Clock Offset:        0.00     seconds
                     Current DOS Drift Rate:     -1.512899 seconds/day
                     Current Total Adjust:       -0.87     seconds

                     Press ESC for Sync Menu, ENTER to ADJUST data:

    In the example above, about half a day has elapsed since the last
    synchronization was performed. As a result of that measurement, JPLCLOCK
    has calculated that the drift rate of the DOS clock is -1.512889 seconds
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 41


    per day and that the current time must be adjusted by SUBTRACTING -0.87
    seconds from the DOS clock. Above these data are four time displays showing
    the present DOS clock (the one being calibrated), the CMOS clock (the
    computer's hardware clock), and the JPLCLOCK time and date both for the
    local time zone and for UTC. The JPLCLOCK time is the time displayed in the
    Main Clock window and reflects the current calculated adjustment from the
    DOS time.
         When using self-calibration, ALWAYS press ESC after viewing these data
    to return to normal operation. If you press ENTER by mistake, press the TAB
    key to leave all items unchanged.
         JPLCLOCK generates a "temporary" automatic synchronization schedule
    during self-calibration, saving the prior schedule (if any). Thus, the
    program will perform the procedure over 7 hours and then revert to the
    original automatic schedule (if automatic synchronization is ENABLED) or
    turn off automatic synchronization (if automatic synchronization is
    DISABLED). You may verify the current status of the automatic
    synchronization from the Main Menu by pressing F10+F3; this will show the
    schedule now in effect; note that the times shown in the schedule are UTC.

                       F1   Execute TIMESET (Manual)
                       F3   Set Automatic Synchronization: ENABLED
                              NEXT TIME = 00:55:00 UTC
                              START     = 08:55:00 UTC
                              INTERVAL  = 04:00:00
                      ESC   Return to Sync Menu
                    ENTER   Resume Program JPLCLOCK

                            Enter selection:

    In the example shown, the automatic synchronization schedule has been set
    to start at 00:55:00 UTC and repeat every four hours. Comparing this
    schedule against the current time, JPLCLOCK will next perform the
    synchronization at 08:55:00 UTC.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 42


    F7   Switch TEXT Mode
    ---------------------

         Function Key F7 permits you to enable or disable the TEXT mode
    provided the text file JPLCLOCK.MSG is present on the current drive and
    directory when the program is started. This command is equivalent to the
    "/TEXT" command line option. If the file JPLCLOCK.MSG has been added while
    using the DOS SHELL (F9), the text will NOT be available since the file is
    read ONLY when JPLCLOCK is started from DOS. Quit program JPLCLOCK and
    restart the program if you wish to add or edit JPLCLOCK.MSG.


    F8   Switch PAGE Mode
    ---------------------

         Function Key F8 permits you to enable or disable the PAGE mode. This
    command is equivalent to the "/PAGE" command line option. Disabling the
    PAGE mode will also disable the TEXT mode if it is currently enabled.


    F9   DOS Shell (DOS 3.3+ ONLY)
    ------------------------------

         Function Key F9 invokes the DOS SHELL, loading a second copy of
    COMMAND.COM and displaying the usual DOS prompt. Most DOS commands and
    programs are now available. To return to JPLCLOCK, type the following at
    the DOS prompt (followed by ENTER):

              EXIT

         Note that using the SHELL with versions of DOS prior to Version 3.3
    may yield unpredictable results. Because program JPLCLOCK remains in memory
    and a second copy of COMMAND.COM is also loaded into memory, the memory
    available to execute programs under the SHELL is considerably reduced. Some
    programs may fail to execute due to insufficient memory or you may receive
    an "Out of Memory" message. If this happens, check to see that all TSR
    (Terminate and Stay Resident) programs that are not required have been
    disabled. If this does not solve the problem, the program in question
    cannot be executed with the shell.
         Except for the potential memory problem, the SHELL operates exactly
    the same as normal DOS. Although JPLCLOCK is resident in memory, it is not
    active. The timer which causes execution of the program to automatically
    resume after some seconds is therefore also NOT active and the computer
    will remain in the SHELL until you type "EXIT" followed by ENTER.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 43


    TIME SYNCHRONIZATION
    --------------------

         As discussed at length elsewhere, the hardware and software clocks on
    the typical personal computer do not keep accurate time. In order to use
    JPLCLOCK in a critical installation such as the JPL Multimission Computer
    Control Center, additional steps must be taken to ensure the accuracy of
    the JPLCLOCK display.

         NOTE: Before proceeding with this section, please read the section DOS
    CLOCK CALIBRATION below. An understanding of that section and its
    procedures is essential before time synchronization is attempted.

         Time synchronization may be accomplished either manually (using the
    DOS TIME command outside program JPLCLOCK) or by using the program TIMESET.
    TIMESET, in turn, may be invoked either on demand or its use may be
    scheduled to occur at any desired interval. The balance of this section is
    concerned with the use of program TIMESET. TIMESET is copyrighted software
    distributed separately, and it must be registered before regular use. See
    the TIMESET documentation for details. (Additional information on TIMESET
    is also given in the section DOS CLOCK CALIBRATION, below.)


    Configuring Program TIMESET
    ---------------------------

         JPLCLOCK has been tested with Professional TIMESET Version 7.2 and may
    not operate correctly with other versions of the program. In particular,
    TIMESET Version 6.0 must be manually configured for standard or daylight
    (summer) time changes each time those changes occur. Read the TIMESET
    documentation, especially if your computer is an 8088/8086 or "non-
    standard".
         Before program TIMESET may be used with JPLCLOCK it must be configured
    for your computer system. If you have not already done so, configure
    TIMESET by entering the following command at the DOS prompt:

              TIMESET /C

         The following configuration screen will be displayed for your
    approval. The information shown here is that used on one of my test
    computers.

              TIMESET Version 7.20 CONFIGURATION
              (C) 1990-1993 Life Sciences Software

                   Outside phone: NULL
               Naval Observatory: 12026530351
                            NIST: 13034944774
                European service: NULL
                 TimeGen service: NULL

                  Your time zone: PACIFIC
                Your time season: DAYLIGHT

                     Serial port: COM1   3F8   IRQ4    (ALL)
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 44


                  Dialing method: TONE
               Dialing baud rate: 1200
                Lock modem speed: NO
                 User's commands: &C1&D2X4

                  Computer clock: DOS CLOCK-CALENDAR

                Auto time season: AUTOMATIC SEASONS U.S.A.
                Manual/auto dial: AUTO NIST (/LAG)
                      Video type: COLOR

         You will probably need to change some of the information shown to
    match your particular computer configuration. Verify that the modem
    information is correct. You WILL need to set your TIME ZONE to the correct
    zone; the Auto time season setting shown will take care of standard and
    daylight/summer time. Make sure the MANUAL/AUTO DIAL is set to AUTO NIST or
    AUTO USNO depending upon the time service you wish to use. Once all data
    are correct, press F10 to save the configured version, then ESC to exit the
    configuration process. TIMESET should now make a call to the selected time
    service; if that call is successful, TIMESET is properly configured.
         The following is a sample screen from a successful TIMESET call:

    +------------------- From NIST.  Connect time: 10.43 sec. --------------------+
    | DATA FOR TIME CALCULATIONS (all data pertain to Coordinated Universal Time) |
    |    Time data string:  49187 93-07-19 00:27:51 50 0 +.6 053.8 UTC(NIST)      |
    |                Date:  07-19-1993                                            |
    |         Julian date:  2449187                                               |
    |         Day of year:  200                                                   |
    |                Hour:  00    Minute:  27    Second:  51                      |
    |                   Daylight Time is in effect in the U.S.                    |
    |        U.S. Standard Time begins on 10-31-1993 at 02:00:00 local time.      |
    +-----------------------------------------------------------------------------+
                                                     System clock set: 17:27:51.01 
    +-----------------------------------------------------------------------------+
    | --------------- ACTION SUMMARY (at instant of timesetting) ---------------- |
    |    Internal delay adjustment:  .01 sec. (added to set time)                 |
    |        Line delay adjustment:  .0538 sec. (precompensated by time service)  |
    |                                                                             |
    |   Universal Time Coordinated:  00:27:51.01           (time at 0ø longitude) |
    |                     UTC Date:  07-19-1993, Monday    (date at 0ø longitude) |
    |                                                                             |
    |      Local computer time was:  17:27:49.53                                  |
    |                       Set to:  17:27:51.01 Pacific Daylight                 |
    |      Local computer date was:  07-18-1993                                   |
    |                       Set to:  07-18-1993, Sunday, Day 199 of 1993          |
    +-----------------------------------------------------------------------------+
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 45


    Time Synchronization Menu
    -------------------------

                          F1   VIEW or SET Time Sync Data
                          F3   TIMESET Time Synchronization
                          F5   MANUAL Synchronization
                         ESC   Return to Main Menu
                       ENTER   Resume Program JPLCLOCK

                               Enter selection:

    Select F1 to view the current time synchronization data or to manually
    execute program TIMESET. Select F3 to enable or disable automatic time
    synchronization using program TIMESET. Select F5 to manually synchronize
    the DOS clock against an external source such as radio station WWV using
    audio tones.


    VIEW or SET Time Sync Data
    --------------------------

                     Current Julian Date:   2448430.351713  06/22/1991
                     Last Synchronized:     2448428.036412  06/20/1991
                     Time since Last Sync:        2.315301 days
                     Current Clock Offset:        0.00     seconds
                     Current DOS Drift Rate:     -3.034839 seconds/day
                     Current Total Adjust:       -7.03     seconds

                     Press ESC for Sync Menu, ENTER to ADJUST data:

    Press ESC to return to the Time Synchronization Menu, or press ENTER to
    adjust the Last Synchronized, Clock Offset, and/or DOS Drift Rate
    parameters. See the section DOS CLOCK CALIBRATION for additional
    information on measuring these parameters. During CALIBRATION or after the
    DOS software clock has been correctly set, do NOT manually adjust these
    data!


    TIMESET Time Synchronization
    ----------------------------

                       F1   Execute TIMESET (Manual)
                       F3   Set Automatic Synchronization: ENABLED
                              NEXT TIME = 16:55:00 UTC
                              START     = 00:55:00 UTC
                              INTERVAL  = 08:00:00
                      ESC   Return to Sync Menu
                    ENTER   Resume Program JPLCLOCK

                            Enter selection:

         Press F1 to immediately execute program TIMESET.
         Press F3 to enable, disable, or change the automatic time
    synchronization function. The sample shown above indicates that the
    automatic function is ENABLED, that it will next occur at 16:55:00 UTC, and
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 46


    that JPLCLOCK will automatically schedule time setting starting at 00:55:00
    UTC each day and at eight hour intervals thereafter. Press ENTER to DISABLE
    the automatic time synchronization feature, or enter the START time and the
    TIME INTERVAL when requested.
         As a general rule and to minimize use of the NIST and USNO telephone
    time services, the longer the synchronizing interval, the more accurate the
    time measurements. This is because the DOS clock ticks occur at 55
    millisecond intervals and in order to maintain the desired accuracy of plus
    or minus 250 milliseconds per day or better, this "granularity" should be
    small compared to the total time used to make the measurements. Where
    practical, I recommend a normal interval of at least 8 hours and preferably
    12 or more hours (after initial calibration).


    MANUAL Synchronization
    ----------------------

                     Current Julian Date:   2448453.693785
                     Last Synchronized:     2448448.302674
                     Time since Last Sync:        5.391111 days
                     Current Clock Offset:       -0.50     seconds
                     Current DOS Drift Rate:     -1.512899 seconds/day
                     Current Total Adjust:       -8.66     seconds

                           (Press ESC to return to Sync Menu)

                     Press: +/= to INCREMENT    - to DECREMENT
                            Z to RESET Offset   S to SET Sync Time

         Manual Synchronization causes JPLCLOCK to present the display shown
    above and to generate a brief tone each second. This may be compared to the
    one second "ticks" generated by radio station WWV and JPLCLOCK's tone
    adjusted in 50 millisecond increments until the two tones occur
    simultaneously. It is my experience that synchronization to within about
    100 or 150 milliseconds may be obtained using this technique.
         Press the "+" or "=" (an unshifted "+" for convenience) key to
    increment the Current Clock Offset, or press the "-" key to decrement the
    Current Clock Offset. When you are satisfied that JPLCLOCK is synchronized
    as accurately as is possible, press the "S" key (upper or lower case) to
    set the synchronization time for use in drift calculations. Press the "Z"
    key (upper or lower case) to reset the Current Clock Offset.
         While not as accurate as using the NIST or USNO Telephone Time
    Services, this method can be used over extended times to calibrate JPLCLOCK
    to reasonable accuracy. The only additional equipment required is a
    shortware receiver capable of receiving WWV, WWVH or a similarly accurate
    time source. WWV and WWVH may be received on the following frequencies:

              2.5 MHz
              5.0 MHz
             10.0 MHz
             15.0 MHz
             20.0 MHz   (WWV only)

    The quality of reception will vary with time of day, atmospheric conditions
    and distance from the transmitter (Fort Collins, CO or Hilo, HI).
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 47


    Propagation delay may be estimated at approximately 5 microseconds per
    statute mile or 5 milliseconds per 1,000 miles, probably not significant
    when performing manual synchronization.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 48


    LAUNCH/HOLD SUPPORT
    -------------------

         JPLCLOCK was originally designed to support long term missions such as
    the Voyager, Ulysses, Magellan, and Galileo spacecraft. It was not intended
    to support fast paced mission events such as the launch of the Space
    Shuttle. One day prior to the actual launch of STS-43, I learned to my
    surprise that the NASA/JPL Multimission Computer Control Center (MCCC) was
    supporting the STS-43 launch of Atlantis and the TDRS-E satellite in real
    time! Charles White at JPL was one of the few people in NASA who was
    relieved that the STS-43 launch was scrubbed on July 31st; it gave him (and
    me) time to prepare an "emergency update" to JPLCLOCK to support real time
    launches. But not too much time -- the launch was rescheduled with only a
    24-hour delay!
         The problem with JPLCLOCK was not that it could not follow a
    preprogrammed scenario such as the ascent timing for a space shuttle
    launch, but that when holds are extended as happened on the scrubbed launch
    attempt it is almost impossible to adjust all of the event times "on the
    fly". Version 9131 addressed this situation by adding a "LAUNCH/HOLD
    SUPPORT" mode which allows the user to force JPLCLOCK to continuously
    adjust all of the mission event times during an extended hold, then release
    the hold coincident with the actual event. The only tricky part is knowing
    what the proper hold times are.
         In order to accommodate this situation, the LAUNCH/HOLD SUPPORT mode
    has been added to JPLCLOCK. With JPLCLOCK operating and the clocks
    displayed on the screen, Function Key ALT-F7 now enables the LAUNCH SUPPORT
    mode. The program requires several entries to support this new mode. A
    sample space shuttle ascent MTD file, STS43F.MTD, is included for testing
    and demonstration.

              Enter KEY TIMER NUMBER [1]:

         Enter the Mission/Event Timer number corresponding to Time Zero. For
         file STS43F.MTD, this is number 42, "STS-43 Launch". Press ENTER to
         accept the default value shown in the square brackets.

              Enter FIRST TIMER to adjust [1]:

         Enter the number of the first Mission/Event Timer whose time is to be
         adjusted. For file STS43F.MTD, this number is the default, 1.

              Enter LAST TIMER to adjust [60]:

         Enter the number of the last Mission/Event Timer whose time is to be
         adjusted. For file STS43F.MTD, this number is 59 (although accepting
         the default value of 60 causes no problems in this case since Timer 60
         is unprogrammed).

              Enter HOLD TIME (HH:MM:SS):

         Enter the POSITIVE time before Time Zero at which you wish JPLCLOCK 
         to hold. For example, if you wish to hold JPLCLOCK at the end of the
         final T-9 minute hold in the launch sequence, enter "00:09". The
         following screen sample illustrates the screen messages which appear.

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 49


              ----------------- LAUNCH SUPPORT -----------------

              Launch Support allows the user to continuously   
              adjust a LAUNCH or HOLD TIME using a KEY TIMER 
              and a set HOLD TIME. When the HOLD TIME releases,
              press ALT-F7 to resume normal operation.

              Enter KEY TIMER NUMBER [1]:       42
              Enter FIRST TIMER to adjust [1]:  1
              Enter LAST TIMER to adjust [60]:  59
              Enter HOLD TIME (HH:MM:SS):       00:09

         Once this information has been entered, JPLCLOCK will adjust the
    selected range of Mission/Event Timers such that the selected Key Mission
    Timer is held at the specified HOLD TIME. The various time of day clocks
    will continue to keep the appropriate time but the Mission/Event Timers
    will appear frozen. The following message will appear below the active main
    timers:

              -------------- LAUNCH/HOLD SUPPORT ---------------

                                 STS-43 Launch

                               COUNT IS HOLDING

                                   -00:09:00

                        Press ALT-F7 to RELEASE HOLD!

         When the instant comes to release the hold, press ALT-F7 again and all
    Mission/Event Timers will resume counting. Note that JPLCLOCK checks to see
    if ALT-F7 has been pressed just before it updates the various times on the
    screen. Therefore, press ALT-F7 just BEFORE the seconds change to the time
    at which the hold is to be released. For example, if the hold is to be
    released at 11:23:00, press ALT-F7 while the clock reads 11:22:59.
         This process may be repeated as many times as necessary during the
    course of a launch. In the past, for example, space shuttle launch holds
    have been extended at T-20 minutes, T-9 minutes, and T-31 seconds. The
    first two times are normal holds and the last is an unscheduled hold which
    is not normally used but which is available if necessary.
         For any of these holds, the HOLD TIME entered should be the time
    remaining before launch when the hold ENDS. The holds at T-20 and T-9 are
    normally ten minutes in duration and the following HOLD TIME should be used
    for these holds:

              T-20 minutes        HOLD TIME = 00:30

              T-9 minutes         HOLD TIME = 00:09
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 50


    DOS CLOCK CALIBRATION
    ---------------------

         The primary purpose of JPLCLOCK is to display the current time and
    other related information in the JPL Multimission Computer Control Center.
    Accuracy and precision in that environment are essential. There is a
    tendency these days to accept whatever a computer says as the absolute
    truth without regard for whether or not the information is even
    "reasonable". For something as basic as time, even an experienced computer
    user often assumes that it is correct. JPLCLOCK attempts to match reality
    with that expectation.
         Given that a computer clock has been set with reasonable accuracy, the
    computer's time will indeed be sufficient for many applications; if you are
    using a word processing or spreadsheet program, knowing the time to within
    a minute or two is probably adequate. For JPLCLOCK, however, this level of
    accuracy simply will not suffice; when used in the Multimission Mission
    Control Center, the information displayed must be correct to within less
    than a second. Unless other steps are taken to set the clock and to
    maintain its accuracy, this will not be the case. No matter how accurately
    the clock on a typical personal computer is set, it will only be a matter
    of hours before the time will have drifted by some seconds. Measured over a
    number of days, the accumulated errors can easily amount to a minute or
    more.
         The timekeeping operations of an IBM-compatible computer are actually
    performed by two separate and independent functions: a clock-calendar
    integrated circuit and lithium battery combination which maintains the
    current time and date in hardware; and a section of the MS-DOS or PC-DOS
    operating system software which maintains the current time and date in
    software. When computer power is off, the hardware chip continues to
    operate using its battery; when the computer is started ("booted"), the
    operating system software reads the hardware clock and sets its internal
    software clock. Absent special software, the DOS time thereafter relies
    entirely on the software clock until the next time the computer is
    restarted. Unfortunately, neither of these clocks was designed for
    accuracy; early versions of the PC did not even include the
    hardware/battery arrangement. Even the typical electric clock, which uses
    the power line frequency for its timekeeping reference, is far more
    accurate.
         The accuracy of the DOS time at any instant is the result of the
    accumulated errors in both clocks. The hardware clock will drift as a
    function of time, temperature, and crystal aging; the software clock will
    gain or lose time depending upon the skill with which its software was
    written and how well that software "cooperates" with the balance of the
    computer's hardware and software. Some software, especially network and
    high speed communications software, can prevent the DOS clock software from
    incrementing when it should, usually resulting in the DOS clock losing
    time. The problem was compounded with the release of DOS Version 3.3;
    beginning with that version, the DOS TIME and DATE commands adjust BOTH the
    hardware and software clocks and thereby potentially eliminate the hardware
    clock as even a modestly reliable reference. If today's personal computers
    used the power line frequency as their primary reference, and only used the
    battery powered crystal oscillator if the power line was not present, clock
    accuracy could at one stroke be improved by at least several orders of
    magnitude.

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 51



    Setting DOS Time
    ----------------

         Bearing these considerations in mind, there are a number of approaches
    to the DOS time question. The most obvious approach, used by the vast
    majority of computer users, is to either ignore the computer clock entirely
    or to say "It's close enough". Regardless of the application, I strongly
    recommend that the DOS clock be set to the approximate time if only to
    assure that files are more or less correctly date stamped. If the accuracy
    of DOS time is important, the computer clock may be set or synchronized
    in a number of ways, some of which are described below. In this context,
    "ACCURACY" means the accuracy of the time setting operation and NOT the
    longer term accuracy of the DOS time.

         1.   TELEPHONE: Many local telephone companies offer a telephone time
              service, usually with a message such as "When you hear the signal
              the time will be ... (beep)". I am not aware of any commercial
              equipment which uses this signal for time setting purposes.

              ACCURACY: Generally plus or minus 5 seconds. With the advent of
              digital voice response equipment, the accuracy has improved in
              recent years to perhaps plus or minus 1 second.

         2.   COMMERCIAL RADIO: Use commercial radio hourly time signals to
              manually set the time. (My experience suggests that the CBS time
              signal is normally quite reliable.)

              ACCURACY: Usually within plus or minus 2 seconds, depending upon
              the source.

         3.   SHORTWAVE RADIO: Time signals are broadcast on shortwave radio
              stations WWV and WWVH by the National Institute of Standards and
              Technology. These time signals may be used to manually set the
              time. WWV and WWVH broadcast on several frequencies: 2.5MHz,
              5MHz, 10MHz, 15MHz, and 20 MHz (WWV only). Reception will vary
              according to your distance from the transmitter, time of day, and
              atmospheric conditions. These time signals are very precise; the
              only major variable is the propagation delay, the time it takes
              the radio signal to travel from the transmitter to your receiver.
              The typical propagation delay is approximately 5 microseconds per
              mile. Outside North America, other national radio services such
              as the British Broadcasting Company's BBC World Service offer
              accurate hourly shortwave time signals.

              ACCURACY: Time setting using WWV or WWVH can usually be performed
              to within about plus or minus 250 milliseconds, of which up to 25
              milliseconds is transmission time and the balance is user
              response time. With practice, plus or minus about 100
              milliseconds is practical.

         4.   NIST/USNO TELEPHONE TIME SERVICE: When real precision and
              accuracy are required, the computer clock may be set remotely
              using the telephone time service of either the National Institute
              of Standards and Technology (NIST, formerly the National Bureau
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 52


              of Standards or NBS) in Boulder, Colorado or Hilo, Hawaii, or the
              U.S. Naval Observatory (USNO) in Washington, D.C. This method
              requires a modem connected to a telephone line and is available
              for systems using DOS version 3.3 or higher AND equipped with
              80286 processor or higher; some 8088-equipped systems may also
              use this method depending upon the type of clock hardware
              installed and the version of DOS being used. The recommended
              method uses the program TIMESET (see below) although other
              similar commercial and shareware programs are available.

              ACCURACY: This is the most accurate method available for setting
              the DOS clocks. Depending upon which service is used, NIST or
              USNO, and whether or not line delay compensation ("lag") is
              employed, the DOS time can be set to within plus or minus 2
              milliseconds. However, since the "time ticks" of the DOS software
              clock occur every 55 milliseconds, or 18.2 times per second, this
              "granularity" effectively limits the accuracy of reading the DOS
              clocks. See the documentation for program TIMESET for additional
              discussion.

         5.   HEATH GC-1000 MOST ACCURATE CLOCK: The GC-1000 is a combination
              digital clock and scanning shortwave radio receiver which may be
              equipped with an RS-232 communications port for use with
              computers and other electronic equipment. This is the only method
              which provides more or less continuous accurate time information.
              RECOMMENDED!

              ACCURACY: When properly configured for your location, equipped
              with an external antenna, used with appropriate computer
              software, and when the receiver is locked to one of the WWV (or
              WWVH) time signals, the GC-1000 can provide time information and
              a standard calibration frequency to an accuracy of plus or minus
              10 milliseconds. When signal lock is lost, the receiver scans the
              5MHz, 10MHZ, and 15MHz broadcasts to reacquire signal and lock.
              Even after signal lock is lost, the receiver maintains an
              accuracy of plus or minus 100 milliseconds for some hours.

         Choose one of the methods suggested or a suitable alternative based
    upon your precision and accuracy requirements. Other methods of maintaining
    an accurate time standard, such an atomic clocks and NIST time code
    equipment, are available -- for a price. Those methods are beyond the scope
    of program JPLCLOCK and this documentation.


    Maintaining DOS Time
    --------------------

         Just in case you missed the point earlier, accurately setting DOS time
    is only half the battle. Even if the DOS time is set very precisely as
    discussed above, all that assures is that the time is correct to the
    required accuracy at that instant. The problem then becomes one of knowing
    how the DOS clocks change or drift with time and how to compensate for
    those changes or, alternatively, checking the DOS time frequently enough
    that any drift on the part of the DOS clocks is acceptable for the intended
    application.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 53


         Of the two clocks in a typical personal computer, the hardware clock
    is considerably more consistent and reliable. I have checked perhaps a
    dozen PC hardware clocks in recent years, and almost all kept reasonably
    good time over a period of several days; as expected, none kept "perfect"
    time. Typical drift rates ranged from about 3 seconds per day to near zero
    seconds per day, with the magnitude and direction of the drift more or less
    constant over the period of measurement. Once a hardware clock has been
    calibrated, therefore, the drift can be calculated with reasonable accuracy
    over periods of some weeks or more; for these results, the computer must
    always be left on and the ambient temperature held constant. Crystal aging
    rates suggest that calibration should be performed at least annually.
         The hardware clock is normally interrogated only when the computer is
    first started or rebooted. The correct time can therefore only be predicted
    at that moment for a calibrated hardware clock and given the last time that
    clock was synchronized with an appropriate time standard. Microsoft
    provides no standard software tools for interrogating the hardware clock at
    other times. Quite the contrary; beginning with DOS Version 3.3, using the
    DOS TIME and DATE commands to set the DOS software clock will also set the
    hardware clock and effectively destroy its usefulness as a calibrated time
    reference. I am at a complete loss to understand the reasoning behind this
    change in DOS; I presume that users were being "confused" by differences
    between the hardware and software clocks; instead of either explaining or
    fixing the problem, Microsoft elected to "legislate" the problem away -- a
    process any politician would recognize instantly. The only mitigating
    consideration is that any really effective solution would probably require
    hardware as well as software changes. Blame IBM, I guess.
         The software clock provides the only time information accessible to
    DOS using standard software. Since this clock is maintained entirely in
    software, with no reference to the hardware clock except at bootup, it is
    at the mercy of other software which may execute from time to time. The
    software clock increments its time using "interrupts", a technique which
    stops a software process in progress just long enough to do the required
    tasks and then resumes the interrupted process. These interrupts occur
    every 55 milliseconds. So long as none is missed, the software clock should
    keep accurate time -- if the software is written correctly and if the
    computer's crystal controlled oscillator is in turn accurate. It may be
    that neither of these conditions is true; certainly the crystal controlled
    oscillator (quite similar to the one which runs the hardware clock) was not
    designed for accuracy or stability. It's original purpose was solely to
    generate the necessary timing signals for the correct operation of the
    computer. Cost, not keeping accurate time, was the primary consideration in
    its design.
         Other software designers have contributed to the problem by writing
    software which, deliberately or inadvertently, prevents the software clock
    from being updated. Off-brand BIOS firmware can present occasional
    problems. Local Area Network (LAN) and high speed communications software
    are typical culprits in this respect. For example, a casual check of the
    clock while using Brooklyn Bridge (a computer-to-computer transfer program)
    indicated that the clock was effectively suspended when data transfers were
    in progress. In one relatively brief period, the DOS clock lost about 30
    seconds.
         As a result of all of these factors, the accuracy of the DOS software
    clock can vary wildly from one computer to the next and from one
    manufacturer to another. One inexpensive "clone" computer that I'd rather
    forget couldn't manage to keep time to better than about 30 seconds per
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 54


    HOUR! Before planning to use a particular computer as a time reference with
    programs like JPLCLOCK, check the computer hardware and software you intend
    to use very carefully.


    Calibrating DOS Time
    --------------------

         Regardless of the method used, the DOS time must be set from time to
    time in order to maintain even reasonable accuracy. More demanding
    applications will require calibration of the hardware or software clock or
    both. The method and frequency of calibration will depend upon your
    accuracy requirements and cost. For my "normal" work, involving program
    development and word processing, I use NIST station WWV and a digital
    PLL shortwave receiver to manually set my computer clocks on a regular
    basis. From time to time I require higher accuracy; given my location in
    California, I usually use a program like TIMESET to call the NIST Telephone
    Time Service in Boulder, Colorado when precise time setting is required.
         When using a program such as JPLCLOCK where consistent accuracy is
    essential over extended periods of time, calibration of the hardware and
    software clocks may be required. I recommend program TIMESET for this
    purpose. TIMESET is a copyrighted program by Peter Petrakis which is     
    distributed using the "shareware" concept. If not available on a     
    convenient bulletin board system, TIMESET may be obtained by writing:

              Life Sciences Software
              8925 271st N.W., Suite 112
              P.O. Box 1560
              Stanwood, WA  98292

              (206) 387-9788

              US$35.00/copy (as of April, 1991)

         TIMESET is an elegant and very precise method for setting the hardware
    and software clocks in your computer. Note that TIMESET sets your computer
    based upon Coordinated Universal Time (UTC) rather than UT1; the offset
    between UTC and UT1 is displayed by TIMESET but is not used. TIMESET is
    superior to any of the several other similar programs I have evaluated. You
    must have a modem and a telephone line connected to your system to use
    TIMESET. Note that the process involves making a telephone call to either
    Boulder, CO or Washington, DC and toll or long distance charges may apply!
    For additional information on configuring TIMESET for use with JPLCLOCK,
    see the section TIME SYNCHRONIZATION.
         The current version of TIMESET, Version 6.0, is not without its
    shortcomings. First, if the modem does not make connection to a telephone
    line correctly, TIMESET may hang indefinitely waiting for a response from
    the modem which will never arrive. This is the case with one of my internal
    modems that is convinced that the first call after initialization is at
    2400 baud; since the call to NIST is being made at 1200 baud, the modem is
    definitely "confused". This problem has not been observed when using a
    standard Hayes 2400 modem. Second, TIMESET does not record the statistical
    results of its operations to a disk file. This means that calibration must
    be performed manually; normal time setting, however, operates automatically
    with no problems. Third, TIMESET does not return an "error code" to
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 55


    indicate whether or not synchronization was successfully performed. I hope
    to convince Mr. Petrakis of the need to address these relatively minor
    problems in an otherwise excellent program.
         The method being used for time synchronization and adjustment will
    determine whether or not calibration of your hardware clock is required. If
    you use the Heath GC-1000 Most Accurate Clock, calibration is probably not
    required. Similarly, if you place a program like TIMESET in your
    AUTOEXEC.BAT file and synchronize your DOS clocks every time you start your
    computer, hardware calibration is not required. If, on the other hand, you
    wish to call NIST as infrequently as possible so as to minimize the
    telephone charges, hardware clock calibration is definitely recommended.
    Unless you use the Heath GC-1000 (or some other time standard) and poll it
    regularly, calibration of the software clock is always required.
         The following suggested calibration procedures assume the use of
    program TIMESET and that TIMESET has already been configured for your
    computer and for your time zone. See the TIMESET documentation for
    instructions. If you use some other program, it must provide similar
    information and you must make appropriate changes to these procedures as
    required by the software actually used.


    Manual Hardware Clock Calibration
    ---------------------------------

         Hardware clock calibration requires a minimum of 48 hours to
    accomplish. The computer should be located in the environment in which it
    is expected to operate and should be turned on and off at the "usual"
    times. The idea is to duplicate the actual operating conditions to the
    maximum extent possible, especially temperature. The following procedure is
    suggested:

         1.   Operate the computer in its normal environment and according to
              its usual schedule for at least 24 hours prior to the test.

         2.   Set the hardware clock using TIMESET according to instructions.
              Use a screen capture program or manually record the ACTION
              SUMMARY prepared by TIMESET. The most significant information is
              shown as:

              Local computer time was:  06:59:41.95
                               Set to:  06:59:44.01 Pacific Daylight
              Local computer date was:  06-19-1991
                               Set to:  06-19-1991, Wednesday

         3.   Operate the computer normally for the next 24 hours. Do NOT use
              the DOS DATE and TIME commands!

         4.   After approximately 24 hours, reboot the computer and repeat the
              time setting with TIMESET and record the same information as in
              Step 2.

         5.   Using the data obtained in Steps 2 and 4, calculate the hardware
              clock drift in seconds per day.

         6.   Operate the computer normally for the next 24 hours. Do NOT use
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 56


              the DOS DATE and TIME commands!

         7.   After approximately 48 hours, reboot the computer and repeat the
              time setting with TIMESET and record the same information as in
              Step 2.

         8.   Using the data obtained in Steps 4 and 7, again calculate the
              hardware clock drift in seconds per day. Repeat as required until
              consistent results are obtained. If consistent results cannot be
              obtained, the selected computer may not be suitable for your
              intended use.

    NOTE: The current version of JPLCLOCK does not directly use the hardware
    clock drift in its time adjustment calculations. This capability will be
    added in a future version. Instead, JPLCLOCK accepts a "Clock Offset" value
    which represents the total hardware clock drift in seconds between the last
    time synchronization was performed and the most recent time the computer
    was booted. If the computer is always synchronized immediately prior to
    running JPLCLOCK, the hardware calibration is not required and the Clock
    Offset should be set to zero.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 57


    Manual Software Clock Calibration
    ---------------------------------

         Manual software clock calibration is quite similar to hardware clock
    calibration and is recommended for all installations using JPLCLOCK which
    do not plan to use the automatic synchronization and calibration features
    of the program. The recommended procedure requires 28 hours to accomplish.
    The computer should be located in the environment in which it is expected
    to operate and should be turned on and off at the "usual" times. The idea
    is to duplicate the actual operating conditions to the maximum extent
    possible, especially temperature. The following procedure is suggested:

         1.   Operate the computer in its normal environment and according to
              its usual schedule for at least 24 hours prior to the test.

         2.   Set the hardware and software clocks using TIMESET according to
              instructions. Use a screen capture program or manually record the
              ACTION SUMMARY prepared by TIMESET. The most significant
              information is shown as:

              Local computer time was:  06:59:41.95
                               Set to:  06:59:44.01 Pacific Daylight
              Local computer date was:  06-19-1991
                               Set to:  06-19-1991, Wednesday

         3.   Operate the computer normally for the next 4 hours. "Normal
              operation" means using the particular software, JPLCLOCK in this
              case, that is planned for the computer. Do NOT use the DOS DATE
              and TIME commands!

         4.   After 4 hours, repeat the time setting with TIMESET and record
              the same information as in Step 2.

         5.   Using the data obtained in Steps 2 and 4, calculate the software
              clock drift in seconds per day.

         6.   Operate the computer normally for the next 12 hours. "Normal
              operation" means using the particular software, JPLCLOCK in this
              case, that is planned for the computer. Do NOT use the DOS DATE
              and TIME commands!

         7.   After 12 hours, repeat the time setting with TIMESET and record
              the same information as in Step 2.

         8.   Using the data obtained in Step 7, again calculate the software
              clock drift in seconds per day. Repeat as required until
              consistent results are obtained. If consistent results cannot be
              obtained, the selected computer may not be suitable for your
              intended use.

         9.   Now enter the latest synchronization date and time (from Step 7)
              and calculated drift (from Step 8 or Step 5) in seconds per day
              into program JPLCLOCK. From the Main Menu, press F10+F1 and enter
              the data as prompted. Enter zero for Clock Offset.

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 58


         Other time sources may be similarly used to calibrate the DOS clock.
    The final result of this calibration should be a software clock drift in
    seconds per day that should remain reasonably stable for relatively long
    periods of time. The calculated clock drift is POSITIVE if your DOS clock
    GAINS time with respect to the time source and NEGATIVE if your DOS clock
    LOSES time with respect to the time source. These data may then be entered
    into JPLCLOCK so that the program will automatically adjust the displayed
    time for the predicted drift.
         Note that the predicted drift calculations assume that JPLCLOCK is
    operating continuously. If you exit JPLCLOCK and perform operations that
    affect the DOS clock (such as disk accesses or high speed communications),
    the drift calculations will still be accurate but you will have to add a
    clock offset to compensate for the DOS clock changes. If you turn off your
    computer, you must reset your clock (to the desired accuracy) and then
    adjust the last synchronization time to correspond to the time you reset
    your computer clocks. For maximum accuracy, perform a manual time
    synchronization (F10+F3+F1 from the Main Menu) each time you reboot your
    computer; JPLCLOCK will automatically update the last synchronization time.
         Program JPLCLOCK is a "well behaved" program written and compiled
    using Microsoft's QuickBASIC Compiler, Version 4.5. No "clever tricks" are
    used to fool the system into doing something that might interfere with
    accurate timekeeping by the DOS software clock. The software clock drift
    obtained by this suggested procedure should be relatively consistent from
    day to day.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 59


    USING TEXT MODE
    ---------------

         In addition to its use in the Multimission Computer Control Center,
    JPL is also considering the use of JPLCLOCK as a means of displaying
    the current mission and event times in other locations at the Laboratory,
    and for display to visitors and guests. In order to explain the data, to
    provide additional commentary on missions in progress, and to provide
    other supplementary information, JPL suggested the addition of a TEXT mode
    to further enhance JPLCLOCK.
         Each time JPLCLOCK is started, it searches for a special message file
    named "JPLCLOCK.MSG" in the current drive and directory. If the file is
    found, it reads the file into memory and thereafter permits the TEXT MODE
    to be enabled. This occurs ONLY when the program is started from the DOS
    prompt; if you use the DOS SHELL (Function Key F9 from the Main Menu) to
    copy or create the special message file, JPLCLOCK will NOT recognize the
    file until the program is restarted.
         The TEXT mode has a capacity of up to 10 screen pages of text with 20
    lines per screen page. The normal distribution of the program includes a
    demonstration message file with the name JPLCLOCK.MSG. To enable TEXT mode,
    you must first enable PAGE mode. This may be done when the program is
    started from the DOS prompt:

              JPLCLOCK /TEXT

    or by using Function Key F7 to enable TEXT mode from the Main Menu.
    Disabling PAGE mode automatically disables the TEXT mode. TEXT mode cannot
    be enabled if the special message file JPLCLOCK.MSG was not found when the
    program was started OR if the file contains no text.
         When the TEXT mode is enabled, JPLCLOCK first cycles through all
    active Mission Timers (as in the usual PAGE mode), then cycles through all
    available text pages in order. The process then repeats. The sample special
    message file contains five text pages.
         When the TEXT mode is active and JPLCLOCK is cycling through all
    active Mission Timers and text pages, a special "bar meter" is displayed
    at the top left of the Mission Timer Windows. This is a row of ten special
    square symbols, one for each of the ten text pages, which indicates the
    status of the page. Each available text page is denoted by a BLUE symbol;
    the active text page symbol is flashing. Inactive text pages (pages without
    any text) are shown with a GRAY symbol.
         In addition to the prepared text in file JPLCLOCK.MSG, the display
    includes a title line with the program version number, the current Julian
    Date, and the local date in conventional notation. The second line displays
    the current UTC Time, Local Time, and the two "bar meters". The left bar
    meter gives the status of title pages, and the right meter the status of
    the Mission Timer pages. The following is the first screen page in the
    supplied sample file JPLCLOCK.MSG. Special "line drawing" characters
    actually used in the display have been replaced in this text by similar
    printing characters.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 60


    | JPLCLOCK by David H. Ransom, Jr.  Version 9141 |  JD2448430.26897 22 JUN 1991
      18:27:19 UTC                      11:27:19 PDT    **********       **********
    ---------- NASA Jet Propulsion Laboratory -------------------------------------

                                  Welcome to JPLCLOCK!
                                  --------------------

                                       Written by
                                  David H. Ransom, Jr.
                                Rancho Palos Verdes, CA


         JPLCLOCK is a real time clock and mission/event timer program written
    especially for the NASA Jet Propulsion Laboratory in Pasadena, California for
    use in the Multimission Computer Control Center (MCCC) and elsewhere in the
    Laboratory. The MCCC is the "nerve center" where all the NASA planetary
    missions such as Magellan, Ulysses, and Galileo are controlled. Other NASA and
    European Space Agency missions are also supported by the JPL MCCC either
    directly or through NASA's Deep Space Network, three large antenna systems
    located in Goldstone, California, near Madrid, Spain and near Canberra,
    Australia. The MCCC is in turn supported by the scientists and engineers at JPL
    and at the California Institute of Technology, which operates JPL for NASA.


    Preparing TEXT Files
    --------------------

         The demonstration message file JPLCLOCK.MSG may be used as a template
    to create customized text files. When preparing text files for use with
    JPLCLOCK, use an ASCII editor, or use a word processor program in the "non-
    document" or "ASCII" mode. Before editing, make a backup copy of file
    JPLCLOCK.MSG. I recommend that all text files for JPLCLOCK be created with
    the filetype ".MSG". Future versions of JPLCLOCK may include a feature to
    read additional text files and the required filetype will be ".MSG".
         The sample file contains 5 screen pages of text. Each screen page
    consists of exactly 20 lines of text, and a maximum of 10 screen pages (or
    200 text lines) is allowed. After creating a new text file (and having made
    a backup copy of the original JPLCLOCK.MSG file!), copy the new file to
    JPLCLOCK.MSG and start program JPLCLOCK in the TEXT mode to view the
    results. My testing indicates that it takes several attempts before the
    appearance of the screen pages suits my taste.
         The TEXT mode displays text lines exactly as it finds them in file
    JPLCLOCK.MSG. As illustrated in the sample file, the "line drawing"
    characters and other special characters are displayed. (Some editors are
    unable to place these special characters in a text file. I recommend the
    shareware editor QEDIT for editing text files for JPLCLOCK.)
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 61


    Modifying JPLCLOCK.INI for Special Features
    -------------------------------------------

                                      CAUTION
                                      -------

         MODIFICATION OF FILE JPLCLOCK.INI IS FOR ADVANCED USERS ONLY!

         If you are not familiar with file editing or do not understand what
         the term "Simple ASCII Editor" means, do not attempt to modify file
         JPLCLOCK.INI.


         File JPLCLOCK.INI may be modified by advanced users to provide two
    special features: force time zone initialization; and, special network
    "read-only" operation. Users modifying this file must use a simple ASCII
    editor or a text editor in the "non-document" mode. Users are cautioned
    that if the file is modified incorrectly, the program may fail to execute
    correctly or may terminate with an error. If this happens, delete
    JPLCLOCK.INI and restart the program. A new JPLCLOCK.INI will automatically
    be created with the correct file format.
         The data items which enable the two special features are contained in
    the first and fourth lines of file JPLCLOCK.INI. All other information in
    the file is maintained by and may be modified from within the program and
    should not be manually altered. The following sample illustrates the first
    four lines of a typical unmodified JPLCLOCK.INI file:

              "9329 ",30015,60
              2448459.25569444,0,0,0,0
              0,0,0,400000000,1,0
              " NASA Jet Propulsion Laboratory ",-8,1,0

         To force JPLCLOCK to re-initialize its UTC Offset and Daylight flags,
    change the first number in the fourth line (following the user's location
    name, "-8" in the sample) to "-99". The changed line would then read:

              " NASA Jet Propulsion Laboratory ",-99,1,0
                                                  ^
                                                  |
                    Force UTC initialization -----+

    This special feature allows a user to create a customized .INI file,
    complete with Location Clocks and Mission/Event Timers, which will force
    any user of the file to enter his correct UTC Offset and Daylight flags.
    Such a file may therefore be freely distributed without regard for the time
    zone of the ultimate user. The distribution version of JPLCLOCK.INI is
    usually modified for this feature.
         In order to use JPLCLOCK on a network server and avoid having users
    intentionally or inadvertently change the .INI and .MTD files, JPLCLOCK may
    be forced into a "read only" mode. In this mode, the program will read but
    not write .INI and .MTD files; menu items are also modified to remove those
    features now disabled. The .INI and .MTD files may also be set to READ-ONLY
    status on the network server as further protection. To force this mode of
    operation, modify the first number on the first line (the version number of
    JPLCLOCK which wrote the .INI file) to a negative number by adding a minus
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 62


    sign. The changed line would then read:

              "-9329 ",30015,60
               ^
               |
               +----- Force Read-Only Network Operation

         After making modifications to JPLCLOCK.INI, be certain to test that
    the modified file executes correctly. Note that JPLCLOCK will remove the
    flag to re-initialize itself (the "-99" on the fourth line) the first time
    it is executed, so perform tests with a copy of the modified file. A file
    which has only been modified for network operation will not be altered by
    execution.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 63


    COMMENTS AND KNOWN PROBLEMS
    ---------------------------

    1.   Computer Processor and Math Coprocessor

         JPLCLOCK has been tested primarily on computers equipped with the
    80286 or higher processor and including a math coprocessor chip. There are
    no known processor-related problems if the computer does NOT have a math
    coprocessor chip but there may be perceptible delays visible on the screen;
    obviously, there's no solution except a faster computer or the addition of
    a math coprocessor chip. Testing on 8088-class machines (the original PC
    and XT computers and their clones) indicates that these computers may skip
    a second from time to time but will otherwise operate correctly. Operations
    involving the CMOS clock/calendar chip will usually fail on these machines
    since their design did not include that feature; the various add-on clock
    chips and circuit cards are usually incompatible with the current clock
    chips. If you have such a computer and wish to use program TIMESET, read
    the TIMESET documentation carefully and test the program thoroughly before
    use with JPLCLOCK.
         Although the calculations performed in JPLCLOCK are almost trivial as
    compared with those required in a complex program such as my satellite
    tracking programs STSORBIT and STSORBIT PLUS, a math coprocessor DOES make
    a difference -- especially in slower PC, XT and AT class machines. Without
    a math coprocessor, the computational overhead required at the beginning of
    each second added to the time required to update the display screen is
    significant, ranging from well over one second in a "basic" PC or XT class
    machine to perhaps half a second in a 6MHz AT class machine. This has two
    major effects: first, the computer may not be able to perform the required
    calculations and update the display each second, causing the display to
    skip a second from time to time; and second, even if the computer is able
    to get everything done in less than one second, the displayed times may
    appear to be delayed by a fraction of a second as compared to the actual
    time and to "ripple" through the various clock and timer displays as they
    are updated. By comparison, an 8MHz AT class computer with math coprocessor
    which I frequently use for testing appears to update all the clock and
    timer displays instantaneously.
         There is no remedy for the first effect on most PC and XT class
    machines although the addition of a math coprocessor will certainly help.
    On most AT class machines, however, adding a math coprocessor will usually
    solve the problem. On all machines, using the large display for local and
    UTC times instead of the small display (with its added features and
    consequent additional computational overhead) will improve or solve the
    problem. For all critical applications, the minimum recommended hardware
    configuration is an AT class computer WITH a math coprocessor chip.
         The second effect, where the screen display is lagging by a fraction
    of a second, can be partially compensated for by adding a fixed Clock
    Offset (use F10+F1 from the Main Menu) so that JPLCLOCK starts making its
    calculations and updating the display slightly BEFORE the actual time to be
    displayed has occurred. For example, if the time updates are lagging by
    half a second from actual time, enter a Clock Offset of -0.5 seconds to
    compensate for the delay. This method will compensate for the time required
    to perform preliminary calculations but cannot change the time required to
    update the screen; further, the Clock Offset can be adjusted to yield the
    "exact" time at only one clock display on the screen. How noticeable this
    problem remains after the Clock Offset adjustment is a function of the
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 64


    display writing speed of a particular computer and its display adapter.

    2.   Computer BIOS Problems

         Media advertizing notwithstanding, not all PC's are created equal. A
    program like JPLCLOCK may execute correctly on one machine and not on
    another. The most likely culprit in these cases is the computer's BIOS
    (Basic Input Output System) which is built into each machine in ROM, Read
    Only Memory, by the manufacturer. Even computers with the same model number
    may have a different BIOS, depending upon when they were manufactured;
    different model numbers by the same manufacturer may perform differently.
    Brands which have demonstrated problems in this area include Tandy, Leading
    Edge, and Ergo. Some computer brands and/or models fail to correctly
    execute ANY program compiled using Microsoft BASIC or QuickBASIC; others
    execute some or all programs correctly but hang and must be rebooted upon
    completion.
         There is no remedy for these problems except to contact the
    manufacturer, report the nature of the problem, and request assistance. As
    a general rule, I can offer little but sympathy. JPLCLOCK has been tested
    on computers ranging from XT-class 8088 systems to the latest 486 systems,
    with and without math coprocessor chips. However, I do appreciate problem
    reports, even those which cannot be solved, so that I may inform other
    users that a problem is known. Please include all pertinent information in
    such reports, including computer manufacturer, model number, DOS version,
    special hardware and/or software, and so forth.

    3.   Monitor Type and Video Adapter Cards

         Not all video adapter cards are created equal either. While most CGA
    adapters perform about the same (slowly!), EGA and VGA adapters can vary
    considerably. The same card, operated in different video modes, can be a
    star or a lemon. There are too many different types of adapters to even
    attempt any generalizations. One practical note: Some VGA monochrome
    monitors "confuse" the VGA BIOS and/or the VGA adapter and require the
    command "MODE CO80" (from the DOS prompt) for proper gray-scale operation
    with JPLCLOCK. If all else fails, include the "/M" command line option to
    force monochrome operation.

    4.   DOS Version and the Shell Feature

         The "Shell to DOS" feature, used by Function Key F9 from the Main Menu
    and when program TIMESET is executed from within JPLCLOCK, is NOT reliable
    for versions of DOS prior to 3.1 and the results of attempting to use these
    features with DOS Version 3.0 and lower are unpredictable. In one case, any
    program compiled using Microsoft BASIC or QuickBASIC failed unless DOS 3.3
    or higher was installed. Some versions of DOS 4.xx are notoriously
    unreliable amd for all versions the DOS 4.x kernel is considerably larger
    than either DOS 3.3 or DOS 5.0; the use of DOS 4.xx is therefore NOT
    recommended. For these and other reasons, I strongly recommend DOS Version
    3.3 or DOS 5.0 as the most stable DOS versions available. DOS 6.0 has been
    used with JPLCLOCK but has not been extensively tested. The "Shell to DOS"
    feature may also fail on certain computers for no apparent reason, probably
    related to the BIOS (see above).

    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 65


    5.   Problems with IBM OS/2

         The IBM operating system known as OS/2 does not implement the clock
    functions in quite the same manner as the Microsoft DOS operating system.
    JPLCLOCK (and Tom Becker's RIGHTIME) are not able to operate correctly with
    OS/2 Version 2.0. Typical problems are an inability to correctly set the
    system clock. When it is available, OS/2 Version 2.1 will be tested. A
    special OS/2 version of RIGHTIME is expected to be available in late 1993.

    6.   Unstable Hardware or Software Clocks

         Some clock circuits have been implemented in such a manner that they
    are essentially a simple tuned resistance-capacitance design which
    effectively ignores the presence of a crystal. Such circuits may drift
    wildly as a function of time, temperature and/or voltage, and make the host
    computer unsuitable for an application such as JPLCLOCK. Any decent crystal
    controlled oscillator should be able to hold to within a second per day,
    but not many PC computer clocks are that good. I've been told that tests on
    a typical PC hardware clock several years ago showed a 5% difference in
    clock frequency when operated on AC power versus the lithium battery. I
    would not have believed that big a difference was even possible with a
    crystal oscillator!
         However, what appears to be an unstable DOS clock may, in fact, be the
    fault of certain software. Network and communications software are
    notorious for turning off the interrupt system and doing other bad things
    which prevent the DOS clock from keeping accurate time. This problem
    usually shows up as a significant time loss AFTER network access or high
    speed communications. Avoid the use of these programs when running JPLCLOCK
    and eliminate any TSR (Terminate and Stay Resident) programs which may
    interfere with the clock.
         The fact that there are two clocks in the PC can cause confusion and
    apparent errors. While JPLCLOCK is running, only the DOS clock is
    interrogated and it is this clock that requires the most careful
    calibration for extended operations. However, each time a computer with a
    battery supported clock/calendar is booted, the hardware clock is used to
    initially set the DOS clock. These two clocks have independent drift
    direction and rate; further, the hardware clock will usually exhibit
    different drift rates when power is on as compared to power off. Thus, the
    time may appear to drift in one direction if the computer is booted
    frequently, and in the opposite direction if it is left on. Microsoft
    compounded the problem by "fixing" the DOS TIME command in Version 3.3 and
    up so that it sets both the hardware and software clocks (for AT-class
    machines and higher), thereby eliminating the hardware clock as any sort of
    a reliable or stable reference!

    7.   Typical Calibration Results

         During the testing of JPLCLOCK I have used both 286 and 386 computers
    and have calibrated each of their software clocks using the NIST telephone
    time service. While the drift rates varied from computer to computer, each
    computer was able to maintain the correct time using JPLCLOCK to within 150
    milliseconds after: a) running for a minimum of 4 hours prior to attempting
    calibration; and b) using a calibration time of at least 4 hours. Since the
    DOS clock ticks occur at 55 millisecond intervals, calibration runs of less
    than four hours will yield an uncertainty which is of the same order of
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 66


    magnitude as the desired calibration accuracy.
         For applications requiring maximum accuracy, these tests indicate that
    the computer should be set using NIST each time the computer is booted and
    then resynchronized at 4 to 24 hour intervals. The stability of the DOS
    clock will determine the optimum interval. JPLCLOCK records the measured
    drift rate each time it makes a synchronization call; use F3+F3+F1 from the
    Main Menu to view the data and adjust the synchronization interval to the
    longest time which yields consistent results. Another consideration is to
    minimize the number of calls to NIST or USNO; these telephone time services
    are a precious resource and should be used as infrequently as possible
    consistent with the needs of your application (as well as your willingness
    to pay the toll charges).

    8.   Color Variations

         Especially with EGA and VGA adapter cards, displayed colors may vary
    considerably from those described. The most common variation is "dim
    yellow" or "brown" (used for the version number on JPLCLOCK's title screen)
    which often appears as either brown or as a dim red which is all but
    indistinguishable from the "real" dim red. Other colors may also vary from
    system to system and from monitor to monitor.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 67


    UTC AND TIME ZONES
    ------------------

         Coordinated Universal Time (UTC) is the world wide civil standard time
    as broadcast by national radio time services such as stations WWV and WWVH
    of the National Institute of Standards and Technology (formerly the
    National Bureau of Standards) and the BBC World Service. It is roughly the
    same as UT1, the time standard used by astronomers and scientists for
    celestial and solar system measurements. However, because the orbital time
    and rotation rate of the Earth is not constant, periodic adjustments of one
    second are required. These adjustments, called Leap Seconds, are usually
    made at the end of June and/or the end of December in order to maintain the
    difference between UTC and UT1 to within 0.9 seconds. As I discovered while
    writing my program ASTROCLK, there are many other defined time standards.
    Because of the ready availability of UTC for synchronization, JPLCLOCK
    assumes that the computer's internal clock is set either to local time or
    to UTC AND that the selected time has a known relationship to UTC.
         The original plan for time zones required each zone boundary to be
    located at the 15 degree meridians around the globe. Since that arrangement
    seldom coincided with national or political boundaries, many adjustments
    have been made over the past one hundred years for political reasons or for
    local convenience. Some time zones are approximately "nominal" while others
    are quite large; all of China, for example, uses a single national time
    zone -- at least officially.
         All civil time zones are related to UTC, usually by an integral number
    of hours (although there are several "half hour zones" and at least one
    "quarter hour zone"). Many countries, including the United States and most
    of Europe, also adjust their civil time by one hour during summer months.
    In the United States, Daylight time begins on the first Sunday in April and
    ends on the last Sunday in October. Other countries use different dates and
    those dates may change from time to time. JPLCLOCK can automatically adjust
    for Daylight time for all time zones in the United States (including Alaska
    and Hawaii) or the change may be performed manually from the Main Menu;
    other time zones must be individually set for standard or summer time.
         The following time zone abbreviations are used by JPLCLOCK for the
    main window and the four location clocks at the lower left of the display
    screen:

        ABBR  OFFSET    ZONE NAME
        ----------------------------------------------------
         UTC       0    Coordinated Universal Time
                        (formerly GMT = Greenwich Mean Time)

         AST      -4    Atlantic Standard Time
         ADT      -3    Atlantic Daylight Time
         EST      -5    Eastern Standard Time
         EDT      -4    Eastern Daylight Time
         CST      -6    Central Standard Time
         CDT      -5    Central Daylight Time
         MST      -7    Mountain Standard Time
         MDT      -6    Mountain Daylight Time
         PST      -8    Pacific Standard Time
         PDT      -7    Pacific Daylight Time
         YST      -9    Yukon Standard Time
         YDT      -8    Yukon Daylight Time
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 68


         HST     -10    Hawaiian Standard Time
         HDT      -9    Hawaiian Daylight Time

         GMT       0    Greenwich Standard Time (UK)
         BST      +1    British Summer Time (UK)
         CET *    +1    Central European Time
         CES *    +2    Central European Summer Time

        AEST *   +10    Australian Eastern Standard Time
        AEST *   +11    Australian Eastern Summer Time
        ACST *    +9.5  Australian Central Standard Time
        ACST *   +10.5  Australian Central Summer Time
        AWST *    +8    Australian Western Standard Time

         * denotes non-standard abbreviation

         Users with specific information on time zone names, abbreviations, and
    and relationship to UTC as well as official times for changing to and from
    daylight/summer time are encouraged to send me that information so that I
    may update or correct the program if necessary. The information will be
    added to subsequent versions of JPLCLOCK.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 69


    FUTURE IMPROVEMENTS AND FEATURES
    --------------------------------

         JPLCLOCK is still a young program and, in addition to repairing the
    inevitable bugs and problems that have been and are yet to be found, I have
    a number of additional features that I hope to add in future releases of
    the program. Here are a few that are being considered:

    1.   Add automatic calibration of the hardware (CMOS) clock comparable to
         that now provided for the software (DOS) clock. This is a little more
         complicated since the hardware clock can only be read to the nearest
         second.

    2.   Add automatic synchronization using the Heath GC-1000 Most Accurate
         Clock. When equipped with an RS-232 interface and external antenna,
         the GC-1000 can maintain an accuracy of plus or minus about 10
         milliseconds with WWV or WWVH. With software overhead, this probably
         translates into about plus or minus 50 milliseconds for the PC, the
         resolution of the DOS clock ticks.

    3.   Give the user the choice of displaying UTC or UT1 (required for
         navigation, for example) if synchronization is done using the NIST
         telephone time service or the Heath GC-1000 Clock (which are the only
         available services which supply the correction from UTC to UT1). The
         current correction is +0.2 seconds as of July 1, 1991.

    4.   For systems equipped with a CMOS clock/calendar chip (286 and higher),
         add the optional capability to use the hardware clock to adjust the
         DOS time when leaving JPLCLOCK to do disk operations, etc.

    5.   Provide an ASCII time message in a format similar to NIST via COM2 at
         a selectable baud rate. The message would be sent every ten seconds
         and synchronized with a final "*" character.

    Some or all of these features may never be added and others may find their
    way to the top of the list first. Some improvements described in prior
    versions of this documentation have already been added. Comments and
    suggestions are welcome!
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 70


    JPLCLOCK REVISION HISTORY
    -------------------------

          Each released version of JPLCLOCK uses a four digit revision code
    such as 9401. The first two digits indicate the year and the second two
    digits indicate the week of the year. In some cases, an additional letter
    suffix is added to distinguish changes occurring within the same week. A
    partial week at the beginning or end of the year is counted as a full week.
    Using this method, a year will typically have 53 weeks although it is
    possible to have 54 weeks in a leap year (1972 is an example). The year-
    week revision code for any date may be determined using the Julian Date
    display, Display Mode 7, in my program ASTROCLK.
         This file records the revision history of program JPLCLOCK through all
    of the minor twists and turns that usually accompany the evolution of such
    a program.  It illustrates the tortuous process of maintaining and refining
    a program as ideas and problems are reported from every quarter. These
    notes may also be helpful to users who are upgrading from one version to
    another to find out what has changed.

                                                  David H. Ransom, Jr.

    9401  January, 1994
    -------------------
    -Added special command line option "/FAFBnn" to show MET in SECONDS for
    Event Timer #nn where "nn" is an active Event Timer number from "01" to
    "60". Example: "/FAFB37" calculated MET from Event Timer #37. Requested by
    Dave Hickman, Space Operations Center 34, Falcon Air Force Base, CO.


    9330A   July, 1993
    ------------------
    -Corrected a fatal error when setting time defaults, F4+F2. Program aborted
    with "Illegal function call ...". The problem was inadvertently introduced
    with the conversion to Visual Basic for DOS (which improved performance but
    which also required that a number of variable names be changed because of
    new reserved words).
    -Corrected a minor display bug which did not show the time elapsed since
    last calibration (F10+F1) when RIGHTIME was active.


    9330    July, 1993
    ------------------
    -This is a MAINTENANCE UPDATE. A number of bugs have been reported over the
    last year and a half. I've tried to squash them all.
    -JPLCLOCK has been modified to use TIMESET Version 7.2 or later which
    includes automatic correction for daylight/summer time. JPLCLOCK now
    executes "TIMESET" rather than the special versions "TIMESTD" or "TIMEDAY"
    required in prior versions. If you are using an older version of TIMESET
    which does not include automatic daylight/summer time correction, you must
    re-configure TIMESET when the time changes occur.
    -Modified the Event/Timer copy process so that the user is requested to
    enter "NEW EVENT/TIMER NAME" after copying data from one event/timer to
    another (with or without a time offset). Press TAB to keep the old name.
    This eliminates the need to modify the name separately.
    -Repaired a bug which caused LAUNCH/HOLD SUPPORT to affect all Event Timers
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 71


    rather than the specified range. This bug has been reported by many users!
    Users should note that there is a ONE SECOND to TWO SECOND delay between
    the time that ALT-F7 is pressed and the time that the count is resumed.
    -Repaired a bug which deleted all Selected Events when the display windows
    were switched with ALT-F5. Thanks to Joe Novak for reporting the problem.
    -Repaired a bug that caused the local and UTC day of the year on the small
    main clock to be blanked out when ALT-F5 was pressed.
    -Changed the color of the blinking active page in Normal Mode from Light
    Magenta to Yellow.
    -JPLCLOCK is now compiled with Microsoft Visual BASIC for DOS. This has
    proven to be a more stable environment than either QuickBASIC or PDS BASIC.
    Unfortunately, a number of variable names had to be changed because of new
    reserved words; hopefully, I didn't introduce any new bugs as a result!


    9209     02/24/92
    -----------------
    -By popular request, I have added a screen blanker function which will turn
    the screen off five minutes after the last keystroke. To enable or disable
    the screen blanker, use Function Keys F4+F5 from the Main Menu or ALT-F2
    while the clocks are displayed. The screen blanker is DISABLED by default
    and the status is preserved in JPLCLOCK.INI. Unlike most screen blankers,
    however, this one restores the screen just before the half hour, at 29 and
    59 minutes past the hour, or press any key.
    -By popular request, I have added Function Keys F3+F4 to enable or disable
    the display of Mission/Event Timer numbers at the lower left of each timer
    window. This function is DISABLED by default. These numbers can be helpful
    during Launch Support and to quickly identify a Mission/Event Timer number
    from the active display.
    -By popular request (yet another one!), I have added the PgUp and PgDn keys
    as active when PAGE mode is disabled (the display is "frozen" to a single
    page of Mission/Event Timers). Previous versions always displayed Page 0 in
    this mode; JPLCLOCK may now display any active page by the use of PgUp and
    PgDn. This status is NOT saved from one execution to the next.
    -The "thermometer" above the Mission/Event Timer windows is now displayed
    at all times, showing the current page and which pages have active timers.
    Pages normally are indicated in GREEN (active and past Time Zero), RED
    (active and not yet to Time Zero), and GRAY (not active). When PAGE mode is
    active, the current page is flashing and all other pages are steady; when
    PAGE mode is NOT active, the current page flashes MAGENTA to so indicate.
    -In order to facilitate network operations, the filename (optionally
    preceeded by the path) for the text message file has been added near the
    end of JPLCLOCK.INI. Since the default is "JPLCLOCK.INI" (and note that it
    should be enclosed in double quotation marks), it is easy to recognize. Use
    any editor in the ASCII or non-document mode. The file is now reloaded each
    time at the beginning of the first text page and may therefore be replaced
    with a new file from time to time without halting program execution.
    -Various minor cosmetic changes.


    9147     11/18/91
    -----------------
    -Corrected a bug which caused the program to hang or generate an error if
    the user loaded an MTD file and set the first timer so that the MTD file
    would attempt to load past Timer #60.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 72




    9141     10/11/91
    -----------------
    -AUTOMATIC DAYLIGHT FLAG now available to switch to daylight savings time
    on the first Sunday in April and back to standard time on the last Sunday
    in October. Use Function Key F4+F1 from the Main Menu. If the computer's
    DOS clock is set to LOCAL time (the default condition) rather than UTC
    time, the DOS clock will also be adjusted.
    -When the DAYLIGHT FLAG is set to AUTOMATIC and the DOS clock is set to
    LOCAL time, the switch and clock setting operations will also be made if
    the computer was off at the designated time and JPLCLOCK is run later; do
    NOT manually adjust your computer's DOS clock for the time switch if the
    DAYLIGHT FLAG is set to AUTOMATIC!
    -When changing the DAYLIGHT FLAG using F4+F1 from the Main Menu, the DOS
    clock will be also adjusted if it is set to LOCAL time.
    -AUTOMATIC and LOCAL/UTC flags added to initial UTC Offset routine.
    -Documented the "force UTC initialization" special feature, present in
    prior versions but undocumented.
    -Added special feature to permit "read-only" operation on network servers
    and added documentation.
    -Added additional on-line help for special function keys active during
    clock display. F1+ENTER from Main Menu.
    -Several other minor problems associated with daylight savings time fixed.
    -Manually entered Mission/Event Timer names were being shortened to 20
    characters instead of 22.
    -UARS (Upper Atmosphere Research Satellite) added to internal default
    database, replacing ROSAT Observatory.
    -The abbreviation in the internal data for MADRID was "MAS" instead of
    "MAD". (Typo in Version 9134.)


    9134      8/18/91
    -----------------
    -Testing completed using MS-DOS Version 5.0. No problems encountered.
    -Changes for LAUNCH SUPPORT, introduced at Version 9131 on an "emergency"
    basis and not fully documented, incorporated in this documentation. File
    JPL9131.UPD deleted from distribution files. See the section LAUNCH SUPPORT
    for details.
    -Launch support enhanced to allow the user to specify the range of
    Mission/Event Timers affected by a countdown hold. More thorough error
    checking added to timer number entries.
    -Corrected bug in SELECTED EVENTS. If a Mission/Event Timer was assigned as
    a SELECTED EVENT and subsequently cleared, incorrect data would be
    displayed for the SELECTED EVENT.
    -Code optimized to the extent practical to improve performance on slower
    computer systems. Even so, operation on XT-class computers is still a bit
    marginal. For all 8088 and 80286 processors, the on-screen clocks may skip
    a second and/or exhibit screen delays depending upon the processor clock
    rate and whether or not a math coprocessor is present.
    - A number of users have reported problems on XT and AT class computers
    without math coprocessors. See the section COMMENTS AND KNOWN PROBLEMS,
    "Computer Processor and Math Coprocessor", for discussion and suggestions.
    -A bug that sometimes caused the page modes to not switch pages at the
    proper time on slow computers has been repaired.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 73


    -Corrected the abbreviations for Goldstone and Madrid to GDS and MAD.


    9131      8/01/91
    -----------------
    -"Emergency Update" for the JPL MCCC to support the launch of STS-43 in
    real time. Details in file JPL9131.UPD.


    9130      7/22/91
    -----------------
    -Changed the PAGE HOLD and PAGE SELECTION logic to accommodate fast paced
    events such as a space shuttle launch. When used in the PAGE mode (use the
    "/PAGE" command line option or F8 from the Main Menu), JPLCLOCK now checks
    each time a page change is scheduled for Mission/Event Timer events due to
    occur within 1 hour, selects the page with events closest to Time Zero,
    jumps to that page, and enters the PAGE HOLD mode. HINT: Set the PAGE DELAY
    (F4+F4 on the Main Menu) to 5 seconds for fastest page scanning.
    -By popular request from amateur radio and BBS operators who keep their
    computers set to UTC, added DOS CLOCK FLAG to select LOCAL or UTC time for
    the DOS CLOCK. With the flag set to LOCAL, JPLCLOCK assumes the computer is
    set to the correct local time (including Daylight Savings Time); with the
    flag set to UTC, JPLCLOCK assumes the computer is set to the correct UTC
    time. The program then performs all necessary time conversions so that the
    correct times are displayed. Set by F4+F2 from the Main Menu.
    -Corrected a minor bug which sometimes displayed Time Zero (0  00:00:00)
    with a RED background instead of a GREEN background. This was caused by a
    rounding problem with the double precision Julian Date.
    -Corrected a minor bug around midnight that might cause the incorrect date
    to be displayed for a few seconds as a function of the calculated Clock
    Offset and Total Drift adjustments.


    9129      7/15/91
    -----------------
    -Added Manual Synchronization using audio tones (F10+F5) to permit
    synchronization using WWV or WWVH. Accuracy of 100 to 150 milliseconds can
    be obtained with practice.
    -Added abbreviations for Australian time zones (with an added "A" prefix
    letter). The abbreviations are the same for STANDARD and for SUMMER time;
    SUMMER time is denoted by an asterisk after the abbreviation. See text for
    details.
    -Corrected bug in HOLD logic (if an event is within 60 minutes ot T-0) that
    caused HOLD to not take effect under certain circumstances.
    -Modified Mission/Event Timer windows to not "blink" if all event data is
    the same from one page to another (that is, when the same event is
    programmed for multiple timers).
    -Modified ALT-F9 so that it both enables the experimental EGA screen font
    and toggles between "large" and "normal" size numbers in the time displays.
    -Added description for MTD files.
    -Various cosmetic changes to the program. Corrections, changes, and
    numerous typographical errors corrected in this text.


    9128      7/05/91
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 74


    -----------------
    -Repaired bug that caused CALIBRATION (F6) to fail to execute subsequent
    TIMESET calls at the correct time interval after the first two. Also
    corrected a sign error in the drift calculation during self-calibration.
    -Corrected screen text for CALIBRATION (F6) to show correct calibration
    intervals of 1, 2, and 4 hours. The total time required is 7 hours.


    9127      7/01/91
    -----------------
    -Added "/SMALL" command line option to display smaller Main Window with
    Local Time and UTC Time. See text for details.
    -Added ALT-F6 during clock display to switch between LARGE and SMALL Main
    Window.
    -Added four additional SELECTED and PRIORITY EVENT windows below the SMALL
    Main Window. User may select: four SELECTED EVENTS (default); two SELECTED
    EVENTS and two PRIORITY EVENTS; or, four PRIORITY EVENTS. Change using ALT-
    F5 when SMALL Main Window is active. These additional four windows are
    displayed ONLY when the SMALL Main Window is selected ("/SMALL" command
    line option or ALT-F6 when clock display is active).
    -Added "/SYNC" command line option to force immediate time synchronization
    (using program TIMESET) when JPLCLOCK is started. The time synchronization
    performed as a result of the "/SYNC" command line option is independent of
    the automatic time synchronization (F10+F3+F3).
    -Changed "/TEXT" command line option so "/PAGE" is no longer also required.
    "/TEXT" now forces PAGE mode.
    -The word "HOLD" now appears above the Mission Timer windows if the current
    page of Mission Timers is being held on the screen because one or more of
    the timers is within 1 hour of its Time Zero.
    -Changed SCREEN FREEZE (ALT-F1) to time out in 5 minutes if no key is
    pressed. Current UTC and Local time are now displayed and updated on line 2
    during the screen freeze. JPLCLOCK will no longer freeze indefinitely!
    -Changed Location Clock prompts for "Uses US Daylight Time" (F2) to "Y" for
    YES and "N" for NO.
    -Corrected bug in Mission Timers: countdown time at zero days displayed "0"
    days rather than "-0" days.
    -Corrected a bug introduced at Version 9126: INI files were interpreted
    incorrectly and reset the Daylight Flag on the Location Clocks which use US
    Daylight Savings Time.
    -In most instances, pressing BACKSPACE will reset the timer in the message
    "JPLCLOCK will start automatically in NN seconds". When typing characters,
    the BACKSPACE will delete the previous character.
    -Modified large clock logic in the Main Window to write only digits that
    have changed. This improves performance with slower computers and/or slow
    video adapter cards.
    -Improved prompts for Read/Write INI & MTD files (F5) and corrected a minor
    bug when ESC was pressed to CANCEL. Added warning that disk operations may
    affect JPLCLOCK's time accuracy.
    -Added warning when exiting to DOS (F9) that disk operations may affect
    JPLCLOCK's time accuracy.
    -Fixed "?" command line help so correct time is shown and added "/TEXT"
    command line reminder.
    -Corrected references to the DOS timer rate. The timer ticks occur 18.2
    times per second or every 54.945 milliseconds. Previous text had the
    frequency given where period was indicated.
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 75


    -Various cosmetic changes.


    9126      6/22/91
    -----------------
    NOTE: Program JPLCLOCK and this documentation were prepared largely from
    memory some hundreds of miles away from my usual references and other
    resources. Technical revisions and corrections can be expected in future
    releases! Comments and suggestions are welcome.
    -INITIAL PUBLIC RELEASE OF JPLCLOCK.
    -Added F10 to Main Menu for manual and automatic time synchronization and
    calibration functions. See the section TIME SYNCHRONIZATION for details.
    -Added automatic offset and drift compensation to JPLCLOCK displayed time
    based upon measured time offset and drift rate. Once the average drift rate
    of the computer's clock is known, JPLCLOCK will compensate for that drift
    and display the corrected time.
    -Added TEXT mode for the display of up to 10 screen pages of supplementary
    information or messages. A sample text file, JPLCLOCK.MSG, has been added
    to the standard distribution files. See text for details.
    -Added "bar meter" above the Main Window to provide countdown to automatic
    time synchronization. Meter appears 100 seconds before JPLCLOCK suspends
    and counts down in increments of 10 seconds.
    -Added two "bar meters" above the Mission Timer windows to display active
    Mission Timer pages and active TEXT pages. The right meter is for Mission
    Timer pages and the left for TEXT pages. Active page markers are in color
    and inactive page markers are gray.
    -Added "#nn" copy format to Mission Timer input (F3).
    -Added TAB to skip an entry and leave it unchanged in several menus.
    -Added F7 to switch TEXT mode from Main Menu.
    -Added F8 to switch PAGE mode from Main Menu.
    -Added ALT-F1 to FREEZE clock display. Press any key to resume operation.
    -Added ALT-F7 to switch TEXT mode from clock display. NOTE: PAGE mode must
    first be enabled before TEXT mode can be enabled.
    -Added ALT-F8 to switch PAGE mode from clock display. NOTE: TEXT mode will
    be disabled (if enabled) when PAGE mode is disabled.
    -Added F4 on the DEFAULTS menu (F4+F4 from Main Menu) to allow the user to
    set the PAGE Delay and the TEXT Delay. See text for details.
    -Swapped Location Windows #2 and #3 to make numbering scheme conform to the
    other windows, top to bottom in a given column.
    -INI file format has changed but JPLCLOCK will correctly read Version 9125B
    INI files and subsequently write the new format. Use F5 from the Main Menu
    to convert prior files; first read the old file then write a new file using
    the same or a new filename.
    -The menu message "JPLCLOCK will start automatically in NN seconds" now
    counts down as the allowed time for keyboard input decreases.
    -Various cosmetic changes and minor bug repairs.
    -Documentation updated.


    9125B     6/16/91
    -----------------
    -Added /PAGE command line option for page mode operation.
    -Number of timers now set to 60 in 10 pages.
    -Mission Timer capacity changed to allow from -9,999 days to +99,999 days
    to accommodate long duration interplanetary missions such as Voyager 1 and
    Program JPLCLOCK: NASA/JPL Multimission Control Center Clock           Page 76


    2 and Pioneer 11 as they leave the solar system.
    -Corrected Daylight Savings Time adjustment and default values for the four
    location clocks.
    -Added Voyager 1 and 2 to default data but times and dates are only
    approximate.
    -Function keys on several menus changed or swapped.
    -Many minor and cosmetic changes.
    -Documentation updated.


    9125A     6/14/91
    -----------------
    -Interim test release.
    -Documentation not updated.


    9125      6/12/91
    -----------------
    -First fully functional release.
    -All configuration features now available.
    -Preliminary documentation released.
    -Mission Elapsed Time for Magellan, Galileo, and Ulysses are NOT correct.
    Dummy values have been used for testing.


    9124      6/10/91
    -----------------
    -Initial BETA VERSION Release. This version was an operational
    demonstration of the program and did not include any configuration
    features.
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