[tz] Fwd: Bulletin C number 57
martin.burnicki at meinberg.de
Fri Feb 1 15:05:25 UTC 2019
Tim Parenti wrote:
> On Fri, 1 Feb 2019 at 07:44, Tony Finch <dot at dotat.at
> <mailto:dot at dotat.at>> wrote:
> Paul Eggert <eggert at cs.ucla.edu <mailto:eggert at cs.ucla.edu>> wrote:
> > One cannot simply translate the IERS file to the NIST file, as the
> NIST file
> > has information that the IERS file lacks, namely, the last time
> that the data
> > were changed.
> Isn't that always 5ish months before the last leap second? :-)
> Well, both have a #$ line, but the purpose is slightly different. For
> NIST, the value is the last time that only the data were changed
> (currently 2016-07-08T00:00:00Z), but for IERS it's the last time the
> file as a whole was updated, including the metadata
> (currently 2019-01-07T14:19:26Z).
Basically the difference shouldn't matter much as long as the data in
the file is correct, and the file has not expired.
If the "last update" time changes whenever *any* of the information in
the file has been updated you can always figure out which is the latest
version of the file, even if an updated file becomes available for some
reason in the middle of the interval between 2 bulletin Cs.
So I'd even say the IERS way to do it makes more sense.
> I would imagine, yes, IERS wouldn't be keen on adopting NIST's practices
> for this line, but I don't necessarily see the reverse change being
> particularly disruptive, if we were to take IERS' file as-is. In the
> worst case, anyone relying on the less-often-updated NIST version of the
> line would just end up pulling the same, unchanged data once every six
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