[LEAPSECS] BBC radio Crowd Science

[Warner Losh]

On Mon, Jan 30, 2017 at 6:06 AM, Tony Finch <dot at dotat.at> wrote:
> Michael.Deckers. via LEAPSECS <leapsecs at leapsecond.com> wrote:
>>
>>    My point was that Arias' labeling makes it clear that the
>>    latest discontinuity in TAI - UTC occurred when TAI assumed
>>    the value 2017-01-01 + 36 s. The ITU labeling (nor any
>>    other specification in ITU-T TF.460-6) does not imply the precise
>>    instant of the discontinuity, nor does IERS Bulletin C52.
>
> It's tricky. Bulletin C is pretty clear about when it thinks TAI-UTC
> changes:
>
>   from 2015 July 1, 0h UTC, to 2017 January 1 0h UTC   : UTC-TAI = - 36s
>   from 2017 January 1, 0h UTC, until further notice    : UTC-TAI = - 37s
>
> However, since there isn't any TAI time with a :60 seconds label, it
> doesn't make much sense to have a defined delta for the last UTC second
> of 2016.

I disagree with this. It makes perfect sense to have a defined delta
for the last UTC second of 2016. And it is 37s because the delta
changes at the start of the positive leap second, or at the start of
the first second after a negative label has been removed. Otherwise
the irregular radix math doesn't work out. It is the change in both
cases that accomplish the leap second. The delta is always defined,
and the points that the delta change lets you know how many seconds
were in that final minute.

Warner