[ntp:questions] Leap second functional question

David L. Mills mills at udel.edu
Fri Feb 22 18:51:00 UTC 2008


Before 1972 there were no leap secconds; however there were periodic 
introductions of tiny rate adjustments relative to Ephemeris Time (ET) 
that drove everybody nuts. There never has been and most likely never 
will be leap deletions. In any case the timecode generators at WWVB and 
WWV cannot handle deletions.

There seems to be widespread misinterpretation on how NTP handles leap 
seconds. Please see: http://www.eecis.udel.edu/~mills/leap.html.

The historical and technical basis for the chronometry and metrology of 
the NTP timescale has been carefully considered and published: 
http://www.eecis.udel.edu/~mills/database/papers/time.pdf. This includes 
the historic introduction of ET, TAI, UTC and leap seconds. There have 
been some attempts to project the Earth wobble into the future, but the 
only reliable predictions now come from the IERS. The historic record of 
the NTP project, inlcuding the adoption of the NTP timescale, has been 
published: http://www.eecis.udel.edu/~mills/database/papers/history.pdf.


Unruh wrote:
> David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:
>>>You are asking for the impossible!  Leap seconds keep time in synch with 
>>That was the intention.  I was pointing out that you can only use "true" 
>>time to represent historic civil times, you cannot calculate the "true" 
>>time of a future civil time beyond the first candidate leap second.
>>>the earth's rotation.  The rate of rotation is subject to small 
>>>variations.  This is why leap seconds occur at irregular intervals and 
>>>why it is possible to have a negative leap second, although I don't 
>>>recall that we ever had one.
>>Exactly, which is why the question casts doubt on the use of "true" 
>>time, which was my intention.
> Well, I suppose one could assume no leap seconds into the future. It is as
> good as UTC which does exactly that, except it also assumes no leap seconds
> into the past, where we know it is wrong. Getting it half right would seem
> an advance.

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