[LEAPSECS] Reliability

[Magnus Danielson]

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