[tz] Lack of "initial" transitions for some zones

Lester Caine lester at lsces.co.uk
Tue Jul 21 18:01:32 UTC 2015

On 21/07/15 18:47, Jon Skeet wrote:
> However, the legacy "root" zones of CET, EET, PST8PDT etc don't have
> this initial "transition" in the file - unless I'm misinterpreting it,
> which is always a possibility.

Since several areas merged to adopt these generic timezones, just which
preceding time does one choose? The zone offset did not exist prior to
it's adoption, and assuming any one offset prior to that is always wrong
for other areas.

> Would it make sense to adjust either the data or zic to make all zic
> output (in the 8-byte-timestamp format, at least) cover all of time? I
> realize that this "extra" data (presumably an insertion of "standard
> time until the first transition") may well not be historically accurate
> - but I doubt that it would be any less accurate than other zones in a
> similar situation.

It will always be less accurate where several areas combined to adopt a
new 'standard' time. The time prior to that may well be 'local mean
time' and tagging THAT is accurate, but then selecting one LMT from
several is always going to be wrong for the rest?

Lester Caine - G8HFL
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