[tz] Dealing with Pre-1970 Data

Lester Caine lester at lsces.co.uk
Sat Aug 31 07:45:11 UTC 2013

Paul Eggert wrote:
> Guy Harris wrote:
>> >If we're obliged to leave them in the tzdb for backwards compatibility purposes, we should:
>> >	accompany them with a disclaimer that they're not actually meaningful

> That sounds reasonable.  Here's a draft of a disclaimer,
> along with a pointer to a discussion of how little
> we know even about solar time if we go back far enough,
> and if it weren't for those amazing Babylonian astronomers
> we'd know even less.  I've pushed this into the
> experimental repository.

Paul - I still object to using 1970 as some magic point at which data came good! 
Just because some legacy systems can't cope with 'negative times' is not a good 
basis. Yes some material needs to be tagged with a level of uncertainty, and 
when putting genealogical timestamps that is normally the case, but much of the 
pre-1970 TIME ZONE information IS accurate? Even after 1970 there is a level of 
inaccuracy - mainly political? - so its almost a case of providing a flag when 
something is disputed?

I do like this particular change but in does only need to be an agreed standard 
for taking location information and creating a time offset? The 'equation' can 
then be used with any location just by feeding the coordinates in, so there is 
no need for a 'database'. In fact, any existing 'location' in the database we 
should be able to access TZ offset, and LMT offset as both have a purpose. When 
someone says 'an hour after midday' the two times may well provide insite to 
some discrepancy!

Lester Caine - G8HFL
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