Rob Seaman skrev:
Adi Stav wrote:
We know that human tolerance to DUT is higher than 20 minutes because we
don't usually bother to compensate for apparent solar time. We know that
it is probably not much higher than one or two hours because time zones
generally have about that resolution. We guess that it is might be about
one hour because many areas in the world choose time zones that are about
one-hour offsets from their local mean time.
These justifications are not necessarily valid, or maybe there are other
or better justifications for smaller DUT maxima. I am just trying to
find out (for myself) what these are. This is why I asked.
Ok (to the second paragraph :-)
Lower limits are hard to pin down. Human tolerance on a particular day
is not the same thing as the tolerance over a year or a lifetime.
Straining a tolerance for one human is not the same as straining it for
6 billion. Human tolerances in general need to be interpreted in terms
of our infrastructure, not just personal perception as we walk from
parking lot to office.
The upper limit has been specified as a "statement against penal
interest" by the ITU. Public enemy number one of leap seconds says an
hour is the upper limit :-)
Embargoing leap seconds (or their equivalent) for periods of decades or
centuries is the same as not making intercalary adjustments at all.
Why is that? Even the Gregorian reform does not come into effect except
every one or two centuries. Yet it is followed exactly.
Gregory revised the Julian calendar. The fundamental standard remains
rooted in what the ancients discovered. The proper comparison is to the
every four year scheduling of leap day opportunities - sometimes those
opportunities remain nulled out, but they still exist.
One should recall that the Gregorian leap day rules where just a
improvement on the static leap day scheme of the Julian calendar so that
it better matched the earths spinning around the sun. They also made a
correction for the accumulate error to restore phase relationships.
This static scheme is not an exact mechanism, as the underlying
mechanism is not exactly mirrored, but rather estimated with sufficient
precission to be usefull over several centuries. Eventually we will need
to revise it again, correct for the accumulated phase error and make an
improved correction algorithm. Essentially, it is not entierly static,
it is infact a dynamic scheme but with a very long time inbetween
adjustments, which is sufficient considering the speed of events.
The adjustments does take time to incoperate, infact some have still not
included them.
The leap second is essentially the same thing, but with a very short
reshedule scheme which unfortunatly coincide with the adjustment
oppertunities being used (actually there is 6 oppertunities on every
decission, but a preference to only use the last). Inbetween we do have
a static scheme. Part of the problem is the life-time of a decision over
the static scheme provided. The actual technicalities of introducing a
leap second would remain the same, but a longer schedule would cause
less of a problem on the issue when they would need to be introduced.
Cheers,
Magnus
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