[tz] subsecond time in Indochina

Steve Allen sla at ucolick.org
Fri Jul 29 17:27:34 UTC 2022

On Thu 2022-07-28T17:01:31-0700 Paul Eggert hath writ:
> Thanks. Sorry to have induced you to go to all that work in digging up
> historical measurements of the Paris Meridian, as the current datum doesn't
> depend on the exact value. It's simpler, I think, to remove that longitude
> from the comments as that will save us the trouble of picking and citing a
> longitude. Done in the attached patch.

Rounding to 0.01 s is the right thing to do.
In the 1920s, the first decade of operation, the BIH only attempted to
specify time differences to 0.01 s between European observatories with
the best clocks and equipment.

The story of time in Indochina must still be richer than is in tzdata.
One of the early radio broadcasts monitored as part of the work of the
BIH was the station in Saigon.  Time signals from Saigon began for the
first World Operation in Longitude during 1926 October/November.
See the picture in the New York Times article from 1925
These were rhythmic signals which provided Greenwich Mean Time, so
time-zone-like time was available to any site with a radio receiver.

Those signals continued routinely until 1941-12-08 when the BIH
described (my translation)
   After 1941 December 8, in effect, the station, only having one emitter,
   found it necessary, on many dates, to sacrifice the time signals for
   exigencies of traffic.

Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street               Voice: +1 831 459 3046         Lng -122.06015
Santa Cruz, CA 95064           https://www.ucolick.org/~sla/  Hgt +250 m

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