[LEAPSECS] Implementation for |UTC-UT1| > 1 s

[Warner Losh]

On Tue, Mar 20, 2018 at 1:59 PM, GERRY ASHTON <ashtongj at comcast.net> wrote:

>
> > On March 20, 2018 at 3:07 PM Warner Losh <imp at bsdimp.com> wrote:
> >
> >
> > On Tue, Mar 20, 2018 at 7:59 AM, GERRY ASHTON <ashtongj at comcast.net>
> wrote:
> >
> > > Perhaps this is too obvious to mention, but if there is a desire to
> allow
> > > |UTC-UT1| somewhat greater than 1 s, but much less than 1 minute, in
> order
> > > to schedule leap seconds further in advance, it will still be
> necessary to
> > > limit each correction to 1 s. This is because a vast number of
> standards do
> > > not allow the number of the second to reach 61.
> > >
> >
> > I don't see how that follows. The number of seconds in a minute is an
> > orthogonal problem ti DUT1, unless you are proposing multiple leap
> seconds
> > at once...
> >
> > Warner
> > _______________________________________________
> > LEAPSECS mailing list
> > LEAPSECS at leapsecond.com
> > https://pairlist6.pair.net/mailman/listinfo/leapsecs
>
> Exactly. It would break lots of stuff if, for example, two leap seconds
> were inserted at the end of December 2022. If there was a desire to predict
> leap seconds a full year in advance, and as of mid-December 2021, it
> appeared there would be a DUT of 1.9 s in December 2022, it would be
> necessary to schedule one leap second at the end of December 2022, and
> another at the end of June 2023.


Nobody, but nobody, is suggesting that there be multiple leap seconds at
once (well, apart from the horrible leap hour idea that should be totally
dead). Having multiple leap seconds at random totally defeats the purpose
of allowing DUT1 > 1. It's to allow longer-term scheduling, not to save
them up and do them all at once (again, the silly leap hour notion should
just be ignored as a fig leaf short-hand for 'never do leap seconds again').

The notion of having a larger DUT1 would still have single leap seconds,
but since the evolution of UT1 is effectively a random walk around a long
term average, it would let you schedule 1 leap second every 18 months for
the next decade and know that you aren't walking off entirely, but that you
might have times where the peak error is > 1s (maybe even > 2s, but
certainly < 1minute). We have extremely good confidence that if we did 7
leap seconds between now and 2028, DUT1 then definitely be  < 10s, almost
certainly be < 5s, quite likely be less than 2s and has a good chance of
being < 1s. All 10-year look-back periods fall into these ranges, at least
since 1972, if my quick eye-balling of the data is right.

Warner
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