Paul Eggert wrote:
Perhaps*replacing* the current "LMT" lines for zones with a line extrapolating the standardized time offsets indefinitely back into the past might be something worth contemplating. If I understand this proposal correctly, it would replace tz's current LMT values with values that are less-precise, since they'd be rounded to the nearest hour somehow. For (say) Paris, this would result in less-accurate data, since it would change Paris's pre-standard-time offset from 0:09:21 to zero. In practice, LMT in Paris before 1891 was, I expect, closer to 0:09:21 than to 0, and I don't see how changing 0:09:21 to 0 would improve the quality of the database entry for Paris.
Skipping the follow on for the moment ... Paul - MY proposal is that if the database returns LMT then it is a flag that we are working with 'pre standard time' dates, and that the actual local time is calculated using a longitude value. For the UK we would have Cardif time, Oxford time and London time simply by providing the correct location. We would still be using the same single zone, and the 'default' would be defined by the location used to tag the zone. Once we move into a time where there is some standardisation, then generally the zone gets a LMTZ tag indicating that it is a time applied across a whole zone. We may still have to handle the problem of 'train time' and 'government time' but this is an historical fact that needs handling anyway and while two zones are required it avoids a proliferation of zones in the 'historic' database. If information turns up that provides more accurate offset to 'local time' than the simple location returns then it's a bridge to cross when it happens, but for now I think this provides a convenient base for consolidating what material we do have available? A simplification may be that the 1970 sub-set just returns 'LMT' so that there is a valid time, but I get the feeling people would prefer what data is available to a cut off set? -- 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