[tz] Before 1970 - proposal to change LMT

Stephen Colebourne scolebourne at joda.org
Mon Aug 11 15:34:51 UTC 2014

On 11 August 2014 15:58, Paul Eggert <eggert at cs.ucla.edu> wrote:
>> All values for the far past are misleading to some degree, "more
>> misleading" is subjective.
> Sure, but all the same it would be weird for a user who does not know that
> LMT means "approximate placeholder" to see a transition like this:
> Zone    Europe/Paris    0:15:00 -       LMT     1891 Mar 15  0:01
>                         0:09:21 -       PMT     1911 Mar 11  0:01
> for France's institution of a standard time zone in 1891.  That would appear
> to be a transition from a GMT-based time zone to a
> let's-thumb-our-nose-at-the-British time zone, which is not at all what
> happened.  In contrast, the (non)-transition that's currently in the
> database feels closer to what actually happened.
> Yes, this is subjective, but the proposed change feels considerably more
> artificial and forced than what we've got.

The question is which is least bad. A smoothed regional value, or an
exact lat/long one.

As I've said before, I don't overly mind keeping lat/long LMT, but if
it is kept it needs to (a) be maintained and (b) have some reasonable

That means an LMT value of some actual relevance to each significant
zone in the database (where significant is at least one zone per ISO
region). Pointing an LMT value across region boundaries is not OK.
Ultimately, the effect of that is to require at least one real zone
(not a link) for each ISO region, something others have requested on
multiple occasions (exceptions could be made for near uninhabited
places like Antarctica, but not for the Carribean or Africa).

Smoothed LMT cross-region or lat/long LMT per region? I don't overly
mind (although smoothed would help many downstream users when they do
request time in the 1700s). However, LMT values that are cross
ISO-region by excessive linking is a conceptual mess.


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