[tz] How good is pre-1970 time zone history represented in TZ database?
Clive D.W. Feather
clive at davros.org
Wed Jun 3 11:21:30 UTC 2020
Alois Treindl said:
> tz_count 24'674'767 data records, 100%
> tz_irange 23'675'636 in time range and region which TZ covers
> correctly, 96%
> tz_good 736'769 in time range and region where TZ is unreliable,
> but correct, 3%
> tz_bad 262'362 in time range and region where TZ database gives
> false result. 1%
> Can you please explain how you've done this analysis. In particular, how do
> you know that TZ is "unreliable, but correct" or gives a bad result?
Okay, to paraphrase what you said:
* "irange" means that the zone that covers the relevant place now covered
it at the relevant time. For example, the Europe/Berlin rules applied at
the relevant time, even if that was pre-1970.
* "good" means that the relevant place had different time rules before 1970
to the zone that now applies, so is in a different zone if you include
pre-1970 rules, but the two zones had the same offset at the relevant time.
For example, the Europe/Berlin rules disagreed with (hypothetical)
Europe/Kiel rules but gave the same result at the relevant time.
* "bad" means that according to the information you hold the relevant place
had a different offset at the relevant time to the zone that now covers it.
For example, Europe/Berlin and Europe/Kiel have different offsets at the
Have I understood correctly?
Clive D.W. Feather | If you lie to the compiler,
Email: clive at davros.org | it will get its revenge.
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