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<div dir="ltr" spellcheck="false" style="">Applying a time stamp to an event in an end-user application with nanosecond accuracy or precision is very difficult because of the problems of measuring the transmission delay from the source to the end-user and the
latency in the end-user application. These problems are generally at least as large as knowing the accuracy of the source with respect to UTC or UTC(lab). Although all of these things can be characterized statistically, that is not of much use for a single
event which cannot benefit from averaging. Note that post-processing may not be of much help in determining the jitter in the processing latency.</div>
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<div dir="ltr" spellcheck="false" style="">The data in Circular T are what they are because of the administrative and processing delays in computing UTC. The UTC(lab) is now and will probably always be an extrapolation, which is limited by the flicker and
random-walk processes of the laboratory time scale. Although the publication of UTCr has decreased the processing delay, it is a provisional scale and is not of much use at the nanosecond level.</div>
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<div dir="ltr" spellcheck="false" style="">Judah Levine</div>
<div dir="ltr" spellcheck="false" style="">Time and Frequency Division</div>
<div dir="ltr" spellcheck="false" style="">NIST Boulder<br>
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On: 10 November 2018 22:24, "Steve Allen" <<a href="mailto:sla@ucolick.org">sla@ucolick.org</a>> wrote:<br>
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<div class="PlainText">On Sat 2018-11-10T19:54:11+0000 Levine, Judah Dr. (Fed) hath writ:<br>
> It is quite challenging to compute time intervals in the pre-1972<br>
> era.<br>
<br>
That depends on the required precision.<br>
<br>
It is still challenging to compute intervals to nanoseconds.<br>
That requires grabbing all the relevant issues of BIPM Circular T<br>
and similar publications of the particular source of time if they<br>
are not members of the BIPM atomic clock club.<br>
<br>
One hundred years ago it was challenging to compute intervals to<br>
centiseconds, and that was the reason for the creation of BIH.<br>
<br>
When Anna Stoyko retired from the BIH in 1965 she published one final<br>
analysis of all the BIH data from 1922 to 1963. She produced plots<br>
showing how the time services of observatories had improved.<br>
<br>
Those plots are reproduced here<br>
<a href="https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fwww.ucolick.org%2F~sla%2Fleapsecs%2Fannastoyko.html&data=02%7C01%7Cjudah.levine%40nist.gov%7C45aee56fa8e74e78eac908d64795e7ed%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636775106502069769&sdata=GrfrVbx5Dg%2Fd6nO2qJzv0U9AHrWHJ3x8aGQ82urQxtU%3D&reserved=0" target="_BLANK">https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fwww.ucolick.org%2F~sla%2Fleapsecs%2Fannastoyko.html&data=02%7C01%7Cjudah.levine%40nist.gov%7C45aee56fa8e74e78eac908d64795e7ed%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636775106502069769&sdata=GrfrVbx5Dg%2Fd6nO2qJzv0U9AHrWHJ3x8aGQ82urQxtU%3D&reserved=0</a><br>
<br>
In order to gather these data the BIH had been monitoring the arrival<br>
times of radio broadcast time signals since 1922. The volumes of<br>
Bulletin Horaire have the numbers that show many ways that various<br>
national observatories and time services messed up (and messed around<br>
with) the time they were providing.<br>
<br>
The data in the issues of Bulletin Horaire are the nightmare of the<br>
tzdb because taken to the absurd limit they would require that tzdb<br>
encode the millisecond-scale differences between the legal civil times<br>
of every nation whose transmitters were monitored by BIH.<br>
<br>
> Different timing laboratories had slightly different values for this<br>
> final time step. The goal was to bring all of the real-time<br>
> realizations of UTC to the same time.<br>
<br>
Well, much closer than before, but if they were the same then the<br>
subsequent issues of BIH Bulletin Horaire and now BIPM Circular T<br>
would be much terser publications.<br>
<br>
--<br>
Steve Allen <<a href="mailto:sla@ucolick.org">sla@ucolick.org</a>> WGS-84 (GPS)<br>
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855<br>
1156 High Street Voice: +1 831 459 3046 Lng -122.06015<br>
Santa Cruz, CA 95064 <a href="https://na01.safelinks.protection.outlook.com/?url=http:%2F%2Fwww.ucolick.org%2F~sla%2F&data=02%7C01%7Cjudah.levine%40nist.gov%7C45aee56fa8e74e78eac908d64795e7ed%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636775106502069769&sdata=xJUyk%2BhmFsoH%2Fpya3BaZT4sDDhp1XEQUTzU12V1CH2I%3D&reserved=0" target="_BLANK">
https://na01.safelinks.protection.outlook.com/?url=http:%2F%2Fwww.ucolick.org%2F~sla%2F&data=02%7C01%7Cjudah.levine%40nist.gov%7C45aee56fa8e74e78eac908d64795e7ed%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636775106502069769&sdata=xJUyk%2BhmFsoH%2Fpya3BaZT4sDDhp1XEQUTzU12V1CH2I%3D&reserved=0</a>
Hgt +250 m<br>
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