[tz] Dealing with Pre-1970 Data

[Guy Harris]

On Sep 1, 2013, at 11:56 PM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> Guy Harris wrote:
> 
>> If it's an entry for Paris, rather than for the French time zone,
>> why don't we have entries for Lyon and Lille and ...
> 
> It's because of the 1970 cutoff.  We would have
> entries such as you describe, if we changed the cutoff
> to (say) 1940 rather than 1970.  Europe/Paris would split
> into 28 zones (if we accept the Shanks data), each with
> its own timestamp history.

But you're probably *still* going to get multiple cities within the same zone even if you change the cutoff to 1911 or even 1891:

	http://vanessafrance.wordpress.com/2012/03/25/a-brief-history-of-french-time/

so the question I'd ask is "why should certain cities be blessed by the tzdb by virtue of having their particular local solar mean time in the database"?

> I agree that the LMT offsets are notional, but even so,
> requiring them to be multiples of an hour feels ahistorical.
> Before standard time was observed people simply didn't set their
> clocks to hour-multiples offsets, and it would be odd
> to pretend that they did.

Then maybe we should just have localtime() return NULL for times prior to the adoption of standard time (as it doesn't take a longitude argument, we can't figure out local time - and even if it *did*, as Steve Allen noted, there might be more than one local time value for a given longitude, unless the longitude indicates which of the two Kansas City jewelers you asked for the time:

	http://news.google.com/newspapers?nid=1499&dat=19451005&id=Sh4aAAAAIBAJ&sjid=-yQEAAAAIBAJ&pg=4415,1664164

) and have mktime() return -1 for those times.