[tz] Stability versus correctness

Lester Caine lester at lsces.co.uk
Fri Jul 11 07:22:36 UTC 2014

On 11/07/14 08:04, Alan Barrett wrote:
> On Thu, 10 Jul 2014, Paul Eggert wrote:
>> I doubt whether there's a genuine lack of concern about accuracy or
>> correctness.  On the contrary, I think we all want the data to be as
>> accurate and correct as it can be.  The only dispute here is how much
>> stability trumps these other concerns.
> Here's where I'd draw the line:  If we obtain new information with
> higher assurance than the old information (or guesses), then we should
> update the database with the new information, for the sake of accuracy. 
> If we believe that the old information has low assurance, but we do not
> have higher assurance information to replace it, then we should leave
> the old information in place, for the sake of stability.
> For example, if you believe that the date that a zone switched from LMT
> to a standard time with a "round number" offset from UT is just a guess
> with low assurance, then leave it alone, until better information
> becomes available; don't link the zone to another zone that was similar
> but had a different "guess" for the data of the switch from LMT to a
> standard time.  If you learn better information, then adjust the
> database accordingly.

I had thought there was an agreement that accurate historic data would
be retained when the previous cull was proposed even though the 1970
limit is used? There are still documented historic updates which have
not been included, and I hope that moving forward as other archives
become available, proven historic data will be incorporated? Some of the
'invented' material IS of concern, but a portion of that is simply a
matter of when a country started using timezones. Exact dates may not be
available but that some historic changes happened is a fact? We just may
never be able to confirm a proven date?

Lester Caine - G8HFL
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