Hi Bob,
Bob Camp wrote:
Hi
I believe that another component that BIPM considers is earth motion data. That data is not quite as common as cesium time scales are. The cesiums keep the agreed upon second tick "right". The earth motion decides when to drop or add a second. It's the drop / add thing that drives all the "we agree with BIPM" language as much as the right time tick stuff.
Actually, that's not the BIPM that deals with that, they acknowledge the
authority of IERS for that aspect.
http://www.bipm.org/en/scientific/tai/tai.html
http://www.iers.org
http://hpiers.obspm.fr/
On a practical basis - my bar is a lot more likely to get busted for having missed a leap second than for being 21 ns off at closing time.
.... and the law enforcers are more likely to miss the leap second than
the average time-nut.
The precision needed to be enforced is mostly never clearly stated, but
for many cases several seconds doesn't make a big difference, and for
closing time of a bar, most places would consider 5 min overtime
pointless to figth about when they want to ensure that it is not on the
scale of hours.
If you are down to miliseconds, what do you legally consider as closed?
Last order served? Last customer out the doors and all doors locked? I
think in practice the law enforcer for that case use their judgement on
the local variant of "closed" and the local variant of tolerance. It's
like porn, we recognise it but it is hard to define it in a legally
meaningful way. The exact border is hard to draw. (A point that Vint
Cerf dressed in his normal IETF three piece suite (he is about the only
one allowed to wear it) made very clear.)
Cheers,
Magnus
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