[tz] historic sub-second time offsets

Steve Allen sla at ucolick.org
Wed Nov 5 15:47:25 UTC 2014

>From their inception the International Time Bureau (BIH) produced
records of the deviations between various time sources.  I have a
sampling of those BIH publications from 1960 in images here

1960 is after the availability of cesium atomic chronometers and
during the era when Heure Definitive was UT2.  These pages include
part of the initial attempt to "coordinate" radio broadcasts between
the US NBS station WWV and the UK NPL station MSF.  They include time
offset plots for various observatories for the entire year of 1960,
and a couple of pages of the radio broadcast offsets for the end of
the year.  Also note that these data were not published until as much
as a year after the measurements, and only then could one know what
time it should have been.

>From the turn of the 20th century it was agreed that everyone would
use the same the technical basis for determining civil time, but the
quality of time available in any particular place depended on
available resources and training, so the implementation was imperfect.
In many countries the observatory time was the legal time, and the
broadcast time signals were, practically, the official time.
Plowing through these historic records of time offsets only makes
sense for projects such as re-reducing occultation data.

The tz database has always eschewed sub-second offsets.
The data on these pages show part of why that is a good thing.


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