On Mon, Sep 26, 2011 at 4:18 PM, <Paul_Koning@dell.com> wrote:
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).
Depending on GMT definition, to my understanding they are already apart.
Because GMT is roughly UT1 while UTC is atomic clock time, and without leap seconds the two drift apart -- right?
To my understanding that is the reason that legal GMT and UTC did already diverge.
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). The file reads:
# Amsterdam Mean Time was +00:19:32.13 exactly, but the .13 is omitted # below because the current format requires GMTOFF to be an integer. # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Europe/Amsterdam 0:19:32 - LMT 1835 0:19:32 Neth %s 1937 Jul 1 -------- That means full seconds. -- Tobias Conradi Rheinsberger Str. 18 10115 Berlin Germany http://tobiasconradi.com/