On 11/10/15 17:19, Guy Harris wrote:
That these rules ONLY apply to time data later than 1970 sweeps the
problem of identifying just were some places were located earlier than that under the carpet, I think that's the intent - to keep it out of scope of the tzdb. As Paul has noted, the further we go back in time, the harder it is to find *correct* time zone information. Go back far enough, and there *is* no standard time, and the "tzid" would end up being a longitude+latitude and you'd just calculate local time from that.
I've no argument with that ... It does not however replace the need for a reliable source of data on when locations started using a standardised time, which has been evolving as more historic material is scanned and translated, and more important where proven reliable pre-1970's data exists but is not provided via tzdb ... If one is working with historic material but other users have a less than complete set of tz data we have confusion when things disagree, so some flag that data is 'unknown' is essential in those circumstances. With tzdist I would contest that tzdb should only be published with a 1970 start date and anything prior to that is unreliable. -- Lester Caine - G8HFL ----------------------------- Contact - http://lsces.co.uk/wiki/?page=contact L.S.Caine Electronic Services - http://lsces.co.uk EnquirySolve - http://enquirysolve.com/ Model Engineers Digital Workshop - http://medw.co.uk Rainbow Digital Media - http://rainbowdigitalmedia.co.uk