[tz] apply Portuguese decree of 1911-05-30
eggert at cs.ucla.edu
Sat Feb 17 00:34:03 UTC 2018
Thanks for the fixes; I installed the attached patch into the
development version on GitHub.
On 02/15/2018 02:05 PM, Michael H Deckers via tz wrote:
> 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.
Thanks, though I'm afraid that the tzdata source doesn't lend itself
well to this kind of detailed provenance annotation, partly because the
data for a transition is partly at the end of one line and partly in the
start of the next line, and there's little room for commentary that
exactly matches the transition. I installed the attached patch, which
uses a less-formal style to mention the 1911 Portuguese decree in every
place that uses it.
While we're on the topic of provenance, I use 'git blame' for tzdb
provenance, and recommend it for doing meta-detective work about why
data entries are the way they are. Although 'git blame' doesn't always
give the info I want, it's convenient and doesn't get in the way of
> [pt 1911] specifies Cabo Verde to use UT - 02 h since 1912-01-01
> 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
> (admittedly, we know from Guernsey on 1913-06-18 that such
> conclusions may be wrong).
For now let's go with your guess, as in the attached patch.
> Note that Lisbon Mean Time as in [pt 1911] and in [Milne 1899] differs
> the GMTOFF given here for it (from Shanks?).
The Shanks-derived offset was wrong, and was fixed in commit
2951fa3bbc8d68e894e96a2399322254e20714a2, first released in 2018a. I
suppose you were looking at a pre-2018a copy of the relevant file.
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