[tz] Request RE: academic research question re: TZ database

Paul Eggert eggert at cs.ucla.edu
Thu Jan 9 01:07:23 UTC 2020

On 1/8/20 11:49 AM, Andrew Lyon wrote:
> It appears that many use the tz database as a source of truth.

Ouch. As we say in big letters, "The tz code and data are by no means 
authoritative." <https://data.iana.org/time-zones/tz-link.html#changes>

> I understand there were 10 years between 1930 and 1941 when the hour of 
> Spring daylight saving transition was 0000 (midnight)  to 0100.  I would 
> like to confirm these entries are in the tz database.

Yes, tzdb says the 10 years 1930/1934 and 1937/1941 all did that, as can 
be seen from the extract Brian emailed.

> I have numerous 
> references that daylight saving time was also observed in 
> America/Regina  during world war ONE ( 1914-1918) and I am uncertain if 
> those entries are in the tz database or the hour of those transitions.

As Brian mentioned, tzdb has these two transitions for 1918:

Sun Apr 14 08:59:59 1918 UT = Sun Apr 14 01:59:59 1918 MST
Sun Apr 14 09:00:00 1918 UT = Sun Apr 14 03:00:00 1918 MDT

Sun Oct 27 07:59:59 1918 UT = Sun Oct 27 01:59:59 1918 MDT
Sun Oct 27 08:00:00 1918 UT = Sun Oct 27 01:00:00 1918 MST

However, there's a good chance these data entries are incomplete for 
Regina. It's also possible that the entries for 1930/1941 are wrong. For 
details, please read the commentary for Regina in the northamerica file. 
Here's the current development version:


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