[tz] TIme in Belize
Michael H Deckers
michael.h.deckers at googlemail.com
Sat Nov 7 15:21:43 UTC 2020
On 2020-11-07 08:18, Paul Eggert wrote:
>
> Unfortunately it's not so clear.
Actually, I think it is quite clear: tzdb should record each official
adjustment (step, discontinuity) of a clock indicating a local civil
time scale. But tzdb should not (and in fact, it cannot) indicate the
true deviation of a local civil time scale from UT or UTC, not only
because the errors in the realizations of UTC or UT used by local
time observatories are very hard to determine, but also because
many of these deviations may consist in differences of rate versus
UT or UTC or in steps of small sizes that could not be represented
with tzdb data anyway.
So the switch in the local civil time for Belize on 1912-04-01 was
from T - 05:52:42.33 h to T - 06 h, where T is the realization of
UT by the timing observatory for Belize at the time. And this is
the fact that tzdb had to represent (possibly up to rounding). That
T must have been off from UT by several seconds is also suggested
by the telegraphy data of Milne, who reports that the Belize Court
House clock was about UT - 05:52:47 h around 1899.)
> One constraint we like to follow is that the LMT longitude corresponds
> to the longitude in zone1970.tab.
This is not mentioned as a constraint and is disliked in many cases.
The modern geographic WGS-84 coordinates can be quite different
from the astronomical coordinates assumed by a time observatory
in a remote place around 1900, so I think it would not be helpful
to add this constraint.
Michael Deckers.
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