S o n o m a U s e r M a n u a l
141
"Smarter Timing Solutions"
Appendix
F
Leap Seconds
UTC stands for Coordinated Universal Time. UTC is the international time standard most commonly
used in the world and is the one used by the Network Time Protocol (NTP). A leap second insertion
is scheduled about every 11⁄2 to three years in order to keep UTC in alignment with the earth’s rota-
tion. Possible leap second insertions can be scheduled at midnight (after 23:59:59) on June 30 or
December 31.
Automatic
Leap Second Insertion
Your GPS-synchronized Sonoma precisely adjusts for leap seconds if and when they occur. There is
nothing you need to do in order to keep your Sonoma time server accurately synchronized to UTC.
You can see the current GPS-UTC parameters that are downloaded from the satellites by using the
gpsutcinfo
command. See
Chapter 9 - Console Port Control and Status
for details on this com-
mand or type
help gpsutcinfo
at the console port.
Background Information
Leap seconds are inserted from time-to-time in order to keep UTC, which is derived from atomic
time (TAI), in agreement with the Earth’s rotation rate. Relative to TAI, the Earth’s rotation rate is
slowing down. This means that UTC must be retarded periodically in order to maintain agreement
between UTC and the apparent daylength. If this were not done, eventually UTC would drift out-of-
sync with Earth’s day and many astronomical and navigational problems would ensue.
The International Earth Rotation Service (IERS) is the organization responsible for measuring the
relationship between UTC and the rotation rate of the Earth. When the difference between UTC and
apparent Earth time has exceeded a certain threshold, the IERS coordinates with the Bureau Inter-
national of the Hour (BIH) to schedule the insertion of a leap second into the UTC time scale. The
IERS publishes
about 6 months in advance of each possible leap second insertion point.
Bulletin C confirms whether a leap second will or will not be inserted at the next possible insertion
point. The IERS website is:
EndRun summarizes this information at this link:
Summary of Contents for Sonoma N12
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