[tz] Issues with pre-1970 information in TZDB
steffen at sdaoden.eu
Thu Sep 23 22:33:14 UTC 2021
Paul Eggert wrote in
<f256f787-9a80-35bc-271b-5269ebf3836f at cs.ucla.edu>:
|On 9/23/21 7:32 AM, Tom Lane via tz wrote:
|> That's half of the issue. The other half is "if a zone does not contain
|> relevant pre-1970 data, how would end users know that?"
|For most users the answer is simple: the pre-1970 data should not be
|relied upon for anything other than an estimate. That data are intended
|only for exact locations named, and most people in the world do not live
|in those exact locations.
|For example, Europe/Berlin is wrong for most of Germany before 1970.
I do not think so? MEZ (CET) was introduced in 1893-04-01, with
clock adjustments all over Germany (-30 .. +30 minute range
i read). This goes so far that GNU date(1) in conjunction with
the IANA TZ displays "date: invalid date X" where X is
00:00:00..00:06:31" for TZ=Europe/Berlin!
|Similarly for Europe/Rome and Italy, Asia/Shanghai and China, etc., etc.
|None of the pre-1970 data should be used for anything important, at
|least not without understanding its severe limitations.
|Luckily for us, tzdb users invariably follow the advice I'm giving here,
|whether consciously or not.
--End of <f256f787-9a80-35bc-271b-5269ebf3836f at cs.ucla.edu>
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
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