[tz] [PATCH 2/3] Replace some zones with links when that doesn't lose non-LMT info.

Steve Allen sla at ucolick.org
Wed Sep 4 21:56:25 UTC 2013

On Wed 2013-09-04T14:40:57 -0700, Paul Eggert hath writ:
> Yeowch!  You're right; sorry about that.  I should have
> written "GMT".  I was misled by zdump's output.

Except that GMT prior to 1925 means one thing for civil
timestamps and a different thing for nautical timestamps.

> Should we change the output of "zdump" etc to fix this
> error?  Currently zdump says "UTC" for old time stamps,
> which isn't correct.  Should it say "UT"
> instead?  Or is even "UT" a bad idea for a time stamp
> in (say) 1627?

Unlike UTC, the concept of UT can be validly extended into the
indefinite past.

> I also should have mentioned that even with GMT,
> my comment was incorrect in some sense.
> Common practice back then for Dutch possessions was
> to use non-integer offsets from GMT, and the tz
> format cannot represent these.  I don't have good
> data for Aruba, but Capt. Thomas Henry Tizard
> of the Royal Navy reported that Curacao's port
> kept time at -04:35:46.9; see Milne 1899.

One might argue over the validity of the conventional formula for UT
being used in the far past, and for the purposes of geodesy it is
relevant to be precise, but to the relevant precision for civil
timestamps any reasonable conventional expression for UT is as valid
as the timestamps themselves.

Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
UCO/Lick Observatory--ISB   Natural Sciences II, Room 165    Lat  +36.99855
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