On 12/10/15 17:55, Paul Eggert wrote:

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you can't use tzdb for reliable conversions prior to 1970!

Not so. Absolutely you can use tzdata, for places like Europe/London in 1915 where the information has been checked and double-checked. True, tzdata is unrelable for *some* locations before 1970, but it's also unreliable for some locations *after* 1970. If you want guaranteed reliability, you're not going to find it in tzdata, nor in any other database out there.

Europe/Jersey and Europe/Guernsey did not follow London during the war and other backzone aliases also vary across Europe in that period Europe/Belfast followed Ireland pre 1968 and like Europe/Isle_of_Man switched to a standard time at a different date to the rest of the UK. All only little point's, but important differences in the pre 1970 chronology! These differences are validated data ... but missing if a distribution simply switches backzone off and while yes some backzone material is unverified, this particular section is very much verified. So how does one recognise that those aliases are returning the correct pre-1970 data and not just mirroring Europe/London or one of the other generic European rule sets? -- 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