[tz] question re zone America/Punta_Arenas in Chile

[Michael H Deckers]

    On 2022-03-16 03:24, Tim Parenti via tz wrote:
> 0002 significantly expands our commentary on Chilean transitions in 1946
> and 1947 and also adjusts LMT/SMT to match Chilean law.  In particular,
> even recent Chilean law still refers to time reckoned as "the meridian of
> the Astronomical Observatory of Lo Espejo, advanced by 42 minutes and 45
> seconds"
> https://www.diariooficial.interior.gob.cl/publicaciones/2018/11/23/42212/01/1498738.pdf


    Thanks for the source, but I think the law is interpreted
    incorrectly in tzdb version 2022a:

    • Law Number 8,522 was promulgated on 1946-08-28, not the day before.

    • That law contains an "artícolo transitorio" which specifies:

            Artícolo transitorio. Al tiempo de entrar en vigor la presente
            ley, se fijará la hora oficial para toda la República con
            arreglo al horário de Verano señalado en el artículo 1.o.

            (Transitional article. At the time when this law takes effect,
            the official time for the whole Republic will be set according
            to summer time as indicated in the 1st article.) [my 
translation]

      That article would be superfluous if the switch to summer time had
      happened on 1946-09-01 (as tzdb currently says) because that
      would have been the switching date already indicated in article 1.
      Thus, the switch to summer time happened earlier than 1946-09-01
      (as wrongly stated by Shanks).

    • That law applies to Punta Arenas as well -- all of Chile had a
      brief summer time period with UT - 04 h until 1947-04-01.

    Hence, both tzdb timezones should be amended:

        Zone America/Santiago  ...
       -     -4:00   1:00    -03     1946 Sep  1 # central Chile
       -     -4:00   -       -04     1947 Apr  1
       +     -4:00   1:00    -03     1946 Aug 29 # central Chile
       +     -5:00   1:00    -04     1947 Apr  1

        Zone America/Punta_Arenas ...
       -     -4:00   -       -04     1947 Apr  1
       +     -4:00   -       -04     1946 Aug 29
       +     -5:00   1:00    -04     1947 Apr  1

    It would take further evidence (such as newspaper clips) in
    order to ascertain the precise hour of the switch in both
    cases. The proposed change implies switches at different
    instants.

    Michael Deckers.