UTC as basis for time legislation

Tobias Conradi tobias.conradi at gmail.com
Mon Sep 26 14:33:03 UTC 2011

On Mon, Sep 26, 2011 at 4:18 PM,  <Paul_Koning at 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 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


More information about the tz mailing list