[tz] User time zones

Zefram zefram at fysh.org
Wed Dec 7 12:09:03 UTC 2011

Alan Barrett wrote:
>This seems fairly useful to me, despite the obvious problems with
>non-unique abbreviations.

There's a conceptual problem regarding what the abbreviation means.
For example, one of the proposed links is BRT -> America/Sao_Paulo.
Sao Paulo has a pattern of DST whereby it's on UT-3h, called "BRT", during
the southern winter, and on UT-2h, called "BRST", during the southern
summer.  So it appears that the real meaning of the "BRT" abbreviation
is a fixed UT-3h.  If a zone named "BRT" has behaviour other than that
fixed offset (and fixed abbreviation), that's going to be surprising.
In fact, the list also suggests BRST -> America/Sao_Paulo, making BRT
and BRST synonymous for that purpose, even though they're clearly not
synonymous in common usage.

This would be even more confusing if, say, "GMT" were interpreted to
mean Europe/London, which switches between GMT (UT+0h) and BST (UT+1h).
Funnily enough, the list does suggest both GMT -> Europe/London and BST
-> Europe/London.

Even for zones that currently are on a fixed offset, historical changes
are a problem.  CHUT -> Pacific/Chuuk yields a surprising interpretation
of "CHUT" prior to 1901.

If you're going to define zones based on the commonly-used abbreviations,
the zones should reflect the actual meaning of the abbreviations.
These don't correspond to existing geographical zones.


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