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IERS Message No. 303                                       June 28, 2016
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NIST UT1 Internet Time Service


The Time and Frequency Division of NIST operates an Internet time server
that transmits UT1 time in the Network Time Protocol (NTP) format. The
server is synchronized to UTC(NIST) by a direct connection to a local
cesium standard. The offset between UT1 and UTC is added to the reply to
a query for the time. The time difference between UT1 and UTC is
obtained from IERS Bulletin A, and the value used by the time server
changes every day at 0 h UTC. The time step at 0 h UTC is generally
about 1-2 ms. This time step is generally too small to be detected by
most users.

The accuracy of the time at the server is approximately 4 ms, and is
determined by the uncertainty in the prediction of the difference
UT1-UTC in the IERS Bulletin A. The accuracy of the time received by a
user will usually be limited by the stability of the network delay from
the user's system to the time server. The overall accuracy of the time
as received by a user will generally be better than 10 ms, and will
often be significantly better than this value.

The name of the server is ut1-time.colorado.edu and its address is
128.138.140.50. The ut1 time service is currently restricted to users
who register with NIST (by e-mail to Judah.levine [at] nist.gov), but it
will be converted to open-access in July, 2016.

The NIST is the US National Institute of Standards and Technology
(http://www.nist.gov/).

Questions or comments to Judah.Levine [at] nist.gov


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