[tz] uptodate data

Tim Parenti tim at timtimeonline.com
Wed Nov 13 19:59:32 UTC 2019


Per theory.html <https://data.iana.org/time-zones/theory.html>, "[a]lthough
a named location in the tz database stands for the containing region, its
pre-1970 data entries are often accurate for only a small subset of that
region."  In particular, pre-1970 data in America/Chicago is only intended
to be correct for Chicago, IL, so timestamps for the example locations you
gave (Duluth, MN; Conway, AR; Port Arthur, TX) may of course differ
according to local custom at the time.

Pre-1970 data is not considered in the scope of the tz project: "Although
1970 is a somewhat-arbitrary cutoff, there are significant challenges to
moving the cutoff earlier even by a decade or two, due to the wide variety
of local practices before computer timekeeping became prevalent."

Tim Parenti

On Wed, 13 Nov 2019 at 03:17, Jean <jc at jcremers.com> wrote:

> I forgot to mention, another famous person Joplin, Janis 19/01/1943
> 09:45:00 Port Arthur TX, United States, 93w57, 29n53, America/Chicago
> Olson database gives the same as astrodatabank, 5 hours. This is to show
> that the results are not consequently wrong. My impression is that the area
> is so big there are expceptions but i'm a layman so..
> On 12/11/2019 21:23, Paul Eggert wrote:
> On 11/9/19 3:51 AM, Jean via tz wrote:
> There are other problems, like the America/Chicago timezone which is
> notorious for giving false results for years before 1970
> Although Matt addressed your other points, I'm curious about this one. In
> what sense is tzdb's America/Chicago "notorious" for being wrong? I used
> Google to search for '"America/Chicago" false results' and the only hits I
> came up with were downstream bugs (e.g., in PHP installation, or in
> mistaken use of Python primitives), not bugs in tzdb itself.
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