[tz] Issues with pre-1970 information in TZDB

Steffen Nurpmeso 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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