[tz] New 'Theory' section "Accuracy of the tz database"

Zoidsoft zoidsoft at gmail.com
Tue Sep 17 04:45:31 UTC 2013

The ACS Atlas would give a clue as to how many would be needed;
approximately 2000 zones in the Olson format would be needed to match what
is in the ACS atlas and it isn't really "complete".  The mapping of time
zones appears mathematically to be like a logarithmic spike with one end
toward relative uniformity (around 400 zones on the low end after 1970) and
the other end to where each clock has its own unique time zone history (aka
LMT).  It is a matter of where you want to draw the line.  The farther in
the past you go toward the date of onset of standard time or LMT the more
chaotic it gets (to the point where it simply would be impossible to have
certainty for many locations).

Due to the fact that most people reside in cities, ACS went about as far as
reasonably possible given the limited manpower.  It was no doubt an
extremely tedious task, but I do wish that they had made their research
methods and criteria for selecting daylight transitions public.  As the
data currently stand, my confidence in transition times for DST for dates
in the first half of the 20th century is shaky at best.  I only feel
relatively confident if it is near the dead of winter or the height of
summer for this period in history.

On Mon, Sep 16, 2013 at 9:32 PM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> Lester Caine wrote:
> > why would there be 'thousands' of new timezones?
> Because, if one defines a "region" to be "a set of geographical
> locations where civil-time clocks have agreed since standard time
> was introduced", there must be thousands of such regions, each
> unique as far as UT-offset history goes.  Shanks identifies
> over 300 such regions for Indiana alone, and most likely he
> missed some.  (Again, I'm ignoring UT offset before standard time
> was introduced, and I'm ignoring the date of transition to standard
> time.)
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