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Re: TimeZones and politics Re: How to tell (in advance) if adate-time is ambiguous?

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July 12, 2017 15:07
Re: TimeZones and politics Re: How to tell (in advance) if adate-time is ambiguous?
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On 11.07.2017 20:50, Bill Ricker wrote:
> On Tue, Jul 11, 2017 at 4:07 AM, Binarus <> wrote:
>> On 10.07.2017 20:14, Eric Brine wrote:
>>> I don't understand the conditions. The law determines when the switching
>>> of offsets from UTC happen, not some person. The switch doesn't happen
>>> at 08:48:27 am in Chicago; it happens at 2am.
>> This point of view is a bit U.S. centric. Indeed, you are describing how
>> it *should* be, but
> We tend to use the timezone nearest us for examples because we're less
> likely to be wrong and thence get dragged into discussing the example
> instead of the concept.

Well, first of all, I did not want to insult or even criticize anybody.
Please forgive me if my wording even made the slightest impression of
doing so - regrettably, I am not a native English speaker.

Actually, I am feeling the highest respect towards the experts who are
helping with the time zone database updates, are bringing them to a
machine readable form and are writing software modules which are dealing
with the overwhelming bunch of time calculating oddities in an
impressive manner. I am really very grateful for that and can't thank
those volunteer experts enough.

I just wanted to say that the statement "... the change happens at 2:00
in Chicago ... " might not be sufficient for my case because I am trying
to write a web application which deals with date and time calculations
in local time zones around the world, and that I'd like the application
to behave well (as far as possible) even in the weirdest cases.

>>  and the next law could determine the switch to
>> happen at 08:48:27 am, and
> It could in theory, but would be beyond atypical.
> (Why? Perhaps a(n) hereditary national leader wants to honor the
> moment of his father's birth?)

Yes, I had something like that in my mind (although I doubt that I will
have the application translated into the languages which are spoken in
such regions :-))

> (The file format and software should handle  08:48,not sure about 08:48:27 ?)

Thanks for the hint. I have never looked into a time zone file yet
(hoping that I could solve all my problems by using modules instead of
doing my own thing).

> [...]
> Do please feel free to use your TZ (or others you know well( in your examples !

I am feeling that it eventually would be better to use the weirdest
examples (risking making a complete fool of myself if missing something)
instead of my time zone (which is Europe/Berlin which has been
well-behaving so far, like America / Chicago, so is probably not an
example I should use to explain my problems ...).

> But don't expect us to be shocked by Venezualan TZ mandates; only the
> short notice made it more eccentric than other isolated half hour
> zones e.g.Newfoundland's UTC-03:30/-02:30. Large expanses of on half
> offset in South Asia and Australia may serve a purpose, but I can't
> explain it.

I have chosen Venezuela because I am not an expert in this field, and it
was the first time I heard of a time shift that was *purely* a political
statement, so I have been shocked backed then. Until the moment when it
happened, I had considered such a thing impossible, so I can still
remember it (and still can't believe it - somehow :-)).

> But AFAIK all TZs to-date that are actually TZs (as in, not Local Mean
> Time, the evil that TZs fixed for the 19thC steam & telegraph Railroad
> schedules) have been at no finer than quarter hour offset from
> GMT/UTC, and mostly hour offsets, with some rather famous half-hours
> (India, Australia) and infamous (Venezuela).
>     The quarter-hour offsets are peculiar and one can only ask "Why?"
> yet always is a Why.  Kathmandu's UTC+05:45 maybe the strangest but is
> still intensely geo-political -- splitting the difference between two
> powerful neighbors,China/Tibet +06 and India(Kolkata) +05:30. Picking
> either could anger the other neighbor, so split the difference.

This is very interesting; I didn't even know that quarter-hour offsets
do exist.

> Yes, it's political.
> But to us here, the output of the political process is our input data
> We try to make things behave as humans will expect according to their
> Quartz Timex  or iPhone Clock app.

And obviously, you are doing so with great success! None of my Linux
servers and applications (written by me or others) never suffered from a
problem due to incorrect time zone data.

And I have learned a lot from your post ...

Thank you very much again,


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