[tz] 1 s error in America/Adak and America/Nome

Paul Eggert eggert at cs.ucla.edu
Sat Jun 10 21:15:46 UTC 2017

On 06/10/2017 07:42 AM, Michael H Deckers wrote:
>    I do not understand the evidence for the proposed changes. A change of
>    time scale by 24 h is only observable though the day of the week and
>    the day number in a calendar (which may be combined with a switch of
>    calendars), but not through the time of day.
>    Where two successive days are observed as Sundays, this is evidence
>    for the change of time scale having occurred at the instant between
>    the two.

Yes. However, the the question is whether America/Sitka should record 
the time kept by those in formal control of Sitka, or the time kept by 
Toomas Ahllund and his fellow workers who made the transition on Sunday 
in order to have a longer weekend. If the former, the transition should 
be at 15:30 Friday (Gregorian); if the latter, it should presumably be 
at 00:00 Sunday (Gregorian). I chose the former, partly because it 
reflects formal transfer of control, and partly because we have a 
specific time-of-day recorded for it.

> And if a precise instant for the acquisition of Alaska is
>    to be taken as the instant of the time zone change, then this 
> assumption
>    should be applied to all locations (where nothing else is known).
>    But the proposed changes to tzdb amount to the change happening when
>       UT = 1867-10-19 + 00:41:37 h for Yakutat
>       UT = 1867-10-19 + 00:31:13 h for Sitka, Juneau, Metlakatla
>       UT = 1867-10-19 + 00:31:03 h for Adak, Nome
>       UT = 1867-10-19 + 00:30:59 h for Anchorage
>    I do not see support for such variations. 

Thanks for reporting that; those were due to bugs in my calculations. I 
installed the attached patch to fix the bugs, and to try to clarify the 
point you mentioned.
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