[tz] Dealing with Pre-1970 Data

Lester Caine lester at lsces.co.uk
Fri Aug 30 08:41:38 UTC 2013

David Patte ₯ wrote:
> Though it has been handy to have some pre-1970 data within the tz database, I
> don't see that it is the best solution for historical tz data in the long run.
> It is clear that that going back far enough in time there is a different LMT for
> every 15 seconds of latitude.

Only since 1884 ;) But even then as Paul as said, timezones where not actually 
agreed on, only where the base UTC time was defined. The 'local time' was still 
synchronised to the sun overhead at noon, hence there was no 'zone'

I think I need to elaborate on why some of this history IS important. Up until 
comparatively recently much historic material has been 'timestamped' by local 
time + location. This makes 'normalising' times for a genealogical comparison 
difficult as one then has to look up information as to the time offset from UTC. 
Sound familiar? PHP has now added a nice 'timezone' facility which provides this 
lookup, and we can NOW store data as UTC timestamp + location and it will 
provide a time display as either local time, UTC or any other location for 
comparison with local events world wide.

Since the PHP offsets are generated currently from TZ the next question would be 
"how does one fix the currently missing data and flag where data IS 
speculation?" Tinkering with 'history' when that has already been used for 
storing normalized data is my own concern. I can probably pass the buck to 
Derick who currently maintains the Date/Time classes, but he simply 'updates' 
from the provided data. Moving forward is it going to be necessary to maintain a 
separate 'history' just to keep data from being corrupted? Adding a version 
stamp to a timezone so we know what was used?

I presume Stephen is doing the same thing in Java, so I am perhaps a little 
surprised if he is now back peddling on getting a common historic base here!

Lester Caine - G8HFL
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