[LEAPSECS] leap second roundup 2017

[Warner Losh]

On Mon, Oct 23, 2017 at 7:28 AM, John Sauter <
John_Sauter at systemeyescomputerstore.com> wrote:

> On Sun, 2017-10-22 at 23:46 -0600, Warner Losh wrote:
> >
> >
> > On Sun, Oct 22, 2017 at 11:02 PM, John Sauter <John_Sauter at systemeyes
> > computerstore.com> wrote:
> > > On Sun, 2017-10-22 at 17:53 -0700, Steve Allen wrote:
> > > >
> > > > The BIPM has contributed
> > > > CGPM draft Resolution "On the definition of Time-Scales"
> > > > For two years various meetings have indicated that a document
> > > like
> > > > this was under construction, so this is probably that result.
> > > >
> > > > A draft of the document seems to be at
> > > > http://www.iaufs.org/CCTF%20Recommendation-DRAFT.pdf
> > > > It largely seems to be a formal way for the CGPM to update the
> > > > definition of TAI and UTC to match what the IAU did over a decade
> > > > ago.
> > > > Unsurprisingly it makes no mention of the connection between the
> > > > calendar day and UT1.
> > >
> > > The next-to-last bullet point under "clarifies that" states that
> > > "UTC
> > > is also a means of dissemination of the standard of frequency;
> > > however
> > > this function is limited to intervals that do not contain leap
> > > seconds;".  Why the concern about leap seconds?  As long as you
> > > know
> > > the name of each second, why should it matter that there is a leap
> > > second in the interval?
> >
> > Because one cannot reliably know that. And by reliably, I mean
> > everybody knows, all the software knows, all the software agrees,
> > even among diverse groups whose primary purpose may not be time
> > keeping and may have sloppy habits about leap seconds (eg, the real
> > world).
> >
> > One can know it, sure, but one cannot count on every single other
> > person who touches the data knowing it with certainty. So it's just
> > best to avoid data that spans a leap second.
> >
>
> By that logic, one should avoid any interval that includes June 30 or
> December 31, since such an interval might include a leap second.


Yes. That's the problem with leap seconds.

Warner
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