[LEAPSECS] Reliability

[Rob Seaman]

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.

The seasonal or diurnal trends in the calendar or clock need to be  
sampled frequently enough to avoid significant quantization errors.   
Leap seconds are productive from this point of view precisely because  
civilians can ignore them.


> By the way, it can be argued that the smoothness property is not  

> strictly

> necessary for calendars. Consider popular and long-used artihmetic

> lunisolar calendars, such as the Hebrew, Hindu, and Chinese calendars,

> that intercalate their years to a resolution of a month.


A very interesting observation.  What calendars does the world really  
depend on for various purposes?  That is, what is the market  
penetration of the Gregorian/Julian calendar?  I would guess nearly  
100% in Europe and North America.  What about the rest of the world?

Rob