[tz] Beginner's help request

Tim Parenti tim at timtimeonline.com
Tue Oct 17 19:00:11 UTC 2017

On 17 October 2017 at 10:23, <Paul.Koning at dell.com> wrote:

> The TZDB is exactly that: a set of rules.

Precisely.  If you're more interested in the rules than individual dates,
you probably want to consume the data files directly (africa, antarctica,
asia, etc.) and then use the rules therewithin to compute dates as far out
as you need.  (zic is the tool developed for this purpose.)  Just keep in
mind, for all the reasons already mentioned, that you should check
regularly for updates whenever possible.

On 16 October 2017 at 08:32, Daniel Ford <dfnojunk at gmail.com> wrote:

> The user can still enter their local DST rules manually, if/when they
> change.

There are a handful of zones for which this can be more complicated than
initially meets the eye.  The cases surrounding the dates of observance of
Ramadan are certainly one such case, though as you note, most such areas
have some sort of *de facto* "buffer zone" around the month for DST
purposes, so the actual lunar observation is less important.  But also note
that this means many of these locations are actually changing their clocks
(possibly) four times a year, and according to two different calendar
systems.  This is something that tz manages to approximate well, but that
would be difficult to expect a typical end-user to program into an embedded
device, if the underlying rules were to be tweaked.

Tim Parenti
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