[tz] apply Portuguese decree of 1911-05-30

Thu Feb 15 22:05:04 UTC 2018

    The decree [http://dre.pt/pdf1sdip/1911/05/12500/23132313.pdf] of 
1911-05-30,
    mentioned for Europe/Lisbon prescribes time zone time scales for 
continental
    Portugal, Madeira, Azores, Cabo Verde, Guinea-Bissau, São Tomé, Angola,
    and Moçambique. It is currently not applied to all of these 
locations, and
    its article 5 is not correctly applied:

      " Art. 5.º Estas disposições entrarão em vigor no instante em que,
          segundo o artigo 2.º, começar o dia civil 1 de [j]aneiro de 1912,
          devendo então todos os relogios ser adeantados ou atrasados
          convenientemente, conforme as alineas seguintes:"...
      --  These dispositions shall enter into force at the instant at which,
      --  according to the 2nd article, the civil day January 1, 1912 
begins,
      --  all clocks therefore having to be advanced or set back 
correspondingly,
      --  conforming with the following sections:....

    (Article 2 specifies the various time zone time scales GMT + 00 h, 
GMT - 02 h,
    etc to be used in Portugal from 1912-01-01 onward.)

    The following proposals contain the necessary corrections. I have also
    tried to indicate exactly which data are implied by the source. I see
    this as a small step to make the tzdb data traceable to its sources, and
    thus to clarify the uncertainty of tzdb data (when they are 
estimated, or
    derived from less reliable sources). The format of these indications can
    certainly be improved.

       +# [pt 1911] decree 
https://dre.pt/pdf1sdip/1911/05/12500/23132313.pdf of 1911-05-30
        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
        Zone  Atlantic/Azores    -1:42:40 -     LMT 1884            # 
Ponta Delgada
       -                         -1:54:32 -     HMT 1912-01-01  # Horta 
Mean Time
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +                         -1:54:32 -     HMT 1912-01-01  02:00u  
# Horta Mean Time
                                 -2:00    Port  -02/-01 1942 Apr 25 22:00s

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
        Zone  Atlantic/Madeira   -1:07:36 -     LMT 1884            # 
Funchal
       -                         -1:07:36 -     FMT 1912-01-01  # 
Funchal Mean Time
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +                         -1:07:36 -     FMT 1912-01-01  01:00u  
# Funchal Mean Time
                                 -1:00    Port  -01/+00 1942 Apr 25 22:00s

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
        Zone  Europe/Lisbon      -0:36:45 -     LMT     1884
       -                         -0:36:45 -     LMT     1912 Jan  1     
# Lisbon Mean Time
       +# [pt 1911] specifies UNTIL date, time & unrounded old 
(-00:36:44.68) and new GMTOFF:
       +                         -0:36:45 -     LMT     1912 Jan  1 
00:00u  # Lisbon Mean Time
                                  0:00    Port  WE%sT   1966 Apr  3  2:00

    The correction for Europe/Lisbon is an example where I think that
    Paul Eggert's proposal for GMTOFF values with fractional seconds
    would be helpful.

    [pt 1911] specifies Cabo Verde to use UT - 02 h since 1912-01-01 02:00Z.
    Currently, tzdb has a switch to UT - 02 h in 1907 without source 
(Shanks by default).
    This switch would precede the one in [pt 1911] which appears to be 
unlikely
    (admittedly, we know from Guernsey on 1913-06-18 that such 
conclusions may be wrong).

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
       -Zone Atlantic/Cape_Verde -1:34:04 -     LMT 1907        # Praia
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +# Ignore [Shanks] specifying UNTIL year 1907, no date, no time.
       +Zone Atlantic/Cape_Verde -1:34:04 -     LMT 1912-01-01  02:00u # 
Praia
                                 -2:00    -     -02     1942 Sep

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
       -Zone Africa/Bissau       -1:02:20 -     LMT     1912 Jan  1
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +Zone Africa/Bissau       -1:02:20 -     LMT     1912 Jan  1  01:00u

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
        Zone  Africa/Sao_Tome     0:26:56 -     LMT     1884
       -                         -0:36:32 -     LMT     1912 # Lisbon 
Mean Time
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +                         -0:36:32 -     LMT 1912-01-01  00:00u # 
Lisbon Mean Time
                                  0:00    -     GMT     2018 Jan  1 01:00

    Note that Lisbon Mean Time as in [pt 1911] and in [Milne 1899] 
differs from
    the GMTOFF given here for it (from Shanks?).

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
       -Zone  Asia/Macau          7:34:20 -     LMT     1912 Jan  1
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +Zone  Asia/Macau          7:34:20 -     LMT 1911-12-31  16:00u
                                  8:00    Macau C%sT

    In backzone:

        # Zone  NAME             GMTOFF   RULES FORMAT  [UNTIL]
        Zone  Africa/Luanda       0:52:56 -     LMT    1892
       -                          0:52:04 -     LMT    1912 Jan  1
       +# [pt 1911] specifies UNTIL date, time & new GMTOFF:
       +                          0:52:04 -     LMT 1911-12-31  23:00u
                                  1:00    -     WAT

    The decree specifies that Goa (Panaji) and Timor (Aisa/Dili) should keep
    the time scale of the adjacent colonies.

    Michael Deckers.