UTC as basis for time legislation

Paul_Koning at Dell.com Paul_Koning at Dell.com
Mon Sep 26 14:18:01 UTC 2011

>> > So if country A says its legal time is an hour ahead of GMT and B says they are an hour ahead of UTC, those are technically different statements.  However, to the approximation of tzdata, the outcome is the same: both country A and B would be shown in the tzdata file as having an offset of 60 minutes.
>> > Is that correct?
>It is correct at present. tzdata doesn't bother with the difference.
>> It is correct under ITU-R TF.460-6.
>> It will not remain true if the draft revision to that document is 
>> approved in its current form at the Radiocommunication Assembly next 
>> January.
>If this happens, then GMT and UTC will start to drift apart. The point at which the tzdata files will take notice of this has not yet been decided (or discussed, I think).

Because GMT is roughly UT1 while UTC is atomic clock time, and without leap seconds the two drift apart -- right?

tzdata gives offsets in units of minutes (no support for fractions of a minute -- see for example the comment on Amsterdam Mean Time in the "europe" file).  So I guess we'd be good for half a century or so.  Or perhaps we'll see the introduction of leap minutes (or leap hours) to replace the former leap seconds...  Or "GMT" might end up being legally redefined as meaning UTC rather than (roughly) UT1.


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