NIST time setting format
The NIST transmits in its own standard Automated Computer Timer Service (ACTS). It is contacted via TCP/IP on port 13. After a setting is made the time string from the NIST used in the setting is displayed in the NIST log window. ClockWatch translates this string. All times from NIST are in UTC.  This time string is made up by a series of fields arranged end to end.

Message Format received from NIST, with an actual sample string below it:

MJD   YYMMDD  HHMMSS DST  LS H ADV MISC
49010 93-01-23 22:01:22  00     0  0  50.0 UTC(NIST) *

MJD  The first number is the date expressed as a Modified Julian Day number (MJD), in the above example 49010 is the Modified Julian Day. The Modified Julian Day: is obtained by counting days from the starting point at midnight on 17 November 1858. It is one way of telling what day it is with the least possible ambiguity.

YYMMDD HHMMSS  The next 6 value pairs give the Universal Coordinated date and time (formerly called Greenwich Mean Time) as year, month, day, hour, minute and second.

DST  The eighth number is the daylight saving time flag, DST. It is based on the continental US system, which has transitions on the first Sunday in April and the last Sunday in October.
DST =  0 means standard time is currently in effect.
DST = 50 means daylight saving time is currently in effect.
DST = 51 means the transition from standard time to daylight time is at 2am local time today.
DST =  1 means the transition from daylight time to standard time is at 2am local time today.
DST > 51 gives advance notice of the number of days to the transition to daylight time.  The DST parameter is decremented at 0000 every day during this advance notice period, and the transition will occur when the parameter reaches 51 as discussed above.
1 < DST < 50  gives advance notice of the number of days to the transition to standard time.  The DST parameter is decremented at 0000 every day during this advance notice period, and the transition will occur when the   parameter reaches 1 as discussed above. The DST parameter is usually not needed for UNIX systems which keep time internally using Universal Time.

Note: ClockWatch uses the Windows internal Time Zone setting to determine if daylight savings time is both used and in effect.

LS       The next number is the leap second flag, LS.
LS = 0 means no leap second is scheduled.
LS = 1 means that a leap second is to be added as 23:59:60 on the last day of the current month.  The last minute will therefore be 61 seconds long. Leap seconds are usually added at the end of either June or December.
LS = 2 means that second 23:59:59 is to be dropped on the last day of the current month.  The second following 23:59:58 will be 00:00:00 of the next day.  This minute will therefore be 59 seconds long.  This situation is unlikely to be necessary in the foreseeable future.
Note that leap seconds are inserted or deleted at the specified Universal Times, while daylight savings transitions are always with respect to local time.

H  The health parameter, H, gives the health of the timeserver:
H = 0 means that the server is healthy.
H = 1 means that the server is operating properly but that its time may be in error by up to 5 seconds. This state should change to fully healthy within 10 minutes.
H = 2 means that the server is operating properly but that its time is known to be wrong by more than 5 seconds.
H = 3 means that the hardware or software have failed and that the time error is unknown.

ADV    The advance parameter, ADV, gives the time advance of the transmissions, in milliseconds.  Each time packet is sent out early by this amount to compensate (approximately) for the network delay.

MISC   The remaining characters on the line identify the time source and are included for compatibility with the ACTS time system.