[tz] Dealing with Pre-1970 Data

Paul Eggert eggert at cs.ucla.edu
Mon Sep 2 05:47:13 UTC 2013

Guy Harris wrote:

> Perhaps *replacing* the current "LMT" lines for zones with a line
> extrapolating the standardized time offsets indefinitely back into
> the past might be something worth contemplating.

If I understand this proposal correctly, it would replace
tz's current LMT values with values that are less-precise,
since they'd be rounded to the nearest hour somehow.  For
(say) Paris, this would result in less-accurate data, since
it would change Paris's pre-standard-time offset from
0:09:21 to zero.  In practice, LMT in Paris before 1891 was,
I expect, closer to 0:09:21 than to 0, and I don't see how
changing 0:09:21 to 0 would improve the quality of the
database entry for Paris.

While I'm on the subject of Paris, local time in France
between 1891 and 1911 was set by law to an offset of 0:09:21
outside train stations, and 0:04:21 inside train stations.
Therefore, any comprehensive attempt to deal with historical
civil time in Paris would need at least two zones.  The tz
database currently uses the outside-of-train-station value.
My source:

French time set back.
New York Times, 1911-03-12, page 15.

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