[tz] time offset for Indochina in 1906

Steve Allen sla at ucolick.org
Fri Jul 29 20:59:51 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.

Not a lot of work.  The Paris/Greenwich offset was a topic of
concern from the 18th century. For most of the story see

> -# the Paris Meridian (2° 20' 14.03" E); the former yields 07:06:30.1333...,
> -# the latter 07:06:29.333..., and for now guess the former,
> +# the Paris Meridian; for now guess the former and round the exact
> +# 07:06:30.1333... to 07:06:30.13 as the legal spec used 66 2/3 ms precision.

This is still bothersome because of that Paris longitude.
A value of 14.03 for the arc seconds is a time value of 9m 20.935 s.
No recent measurement had a value that large.
Using either 20.93 or 20.932 for the Paris Observatory
the offset of this zone in 1906 would be

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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