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6000-100AppE.fm Rev. D TimeVault User’s Manual E-125
E
Automated Computer Time Service (ACTS)
The Automated Computer Time Service (ACTS) is run by the National Institute of
Standards and Technology (NIST) in Boulder, Colorado.
ACTS allows computer users with modems to synchronize their clocks by telephone. The
phone number for ACTS is (303) 494-4774 (not toll free). Users can connect at speeds of
up to 9600 baud with 8 data bits, 1 stop bit, and no parity and obtain time signals with
standard uncertainty of 5 ms. To receive the full time code, you must connect at a speed
of at least 1200 baud.
The full time code is transmitted every second and contains more information than the
300 baud time code, which is transmitted every 2 seconds. The full time code looks like
this:
JJJJJ YRMODA HH:MM:SS TT L DUT1 msADV UTC(NIST) OTM
where
JJJJJ = the Modified Julian Date (MJD). The MJD is the
last five digits of the Julian Date, which is the
number of days since January 1, 4713 B.C. To get
the Julian Date, add 2.4 million to the MJD.
YRMODA = the date, showing the last two digits of the year, the
month, and the current day of month.
HH:MM:SS = the time in hours, minutes, and seconds. The time is
always sent as Coordinated Universal Time (UTC).
An offset needs to be applied to UTC to obtain local
time. For example, Mountain Time in the U. S. is
7 hours behind UTC during Standard Time, and
6 hours behind UTC during Daylight Saving Time.
TT = a two digit code (00 to 99) that indicates whether the
United States is on Standard Time (ST) or Daylight
Saving Time (DST). It also indicates when ST or
DST is approaching. This code is set to 00 when ST
is in effect, or to 50 when DST is in effect. During
the month in which the time change actually occurs,
this number decrements every day until the change
occurs. For example, during the month of October,
the U.S. changes from DST to ST. On October 1,