[tz] Dealing with Pre-1970 Data

Lester Caine lester at lsces.co.uk
Fri Aug 30 22:03:52 UTC 2013

Guy Harris wrote:
> 	not create any new tzdb zones if the only reason for the new zone is "before standard time was established, these two locations had different LMT".
I have no problem with that.
I see no reason for LMT being returned when looking for a TZ offset, but there 
is well documented TZ data prior to 1970 which should be retained and returned.
The various API's simply need to switch to an alternative when a date is prior 
to 'known timezone time', but we are probably going to argue if that date is 
1884 or something later? Certainly some of the links provided have shown the 
politics involved so nothing has changed there :)

> Historical rules*subsequent to*  time zone establishment, however, are arguably worth keeping and perhaps even updating, albeit perhaps with a disclaimer saying we can't guarantee historical accuracy and/or that they are subject to change due to additional historical information being found.
There are notes as to the accuracy of some data and that is all one can do. It's 
that material that we were fighting to maintain the independence of recently?

Personally I can see a future linkup here with the historic mapping fork on 
openstreetmap. The various changes over time to both the timezone bands, and the 
daylight saving areas need to be documented and linked to the chronology so that 
one can track the changes at any location. This is where I would expect LMT to 
be generated since location is accurately defined, and while the Greenwich 
Meridian only came into being in 1884, there is perfect sense in 'mapping' times 
prior to that based on the offset of midday from it for earlier times? This is 
also an historically correct fact once clocks were being used and synchronising 
that with the latter zero of UTC is just logical? Now WHEN was the sun dial 
invented :)

Lester Caine - G8HFL
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