[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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