[LEAPSECS] Terminology question
sla at ucolick.org
Wed Mar 10 12:54:38 EST 2010
On Wed 2010-03-10T16:05:28 +0000, Michael Deckers hath writ:
> On 2010-03-09 17:34, Zefram wrote:
> > Apparently not. I'm inclined to use the phrase "faux linear time".
> > These timescales are really encodings of UTC-wise broken-down time, but
> > they sufficiently resembles a linear timescale that it's commonly mistaken
> > for one. I think it's worth reminding people clearly of the reality.
> Perhaps "piecewise linear" may also be appropriate -- it is a
> common term in math. TAI - UTC (after 1972) may then be called
> a "step function", which is a "piecewise constant" function.
Except that to say that any available form of UTC is linear
is to invalidate its use as a precision time scale.
Read BIPM's Circular T.
Follow the link to BIPM's TT(BIPM09)
Plot the numbers. It's not linear.
All precision time scales must employ empirical lookup tables.
Leap seconds are just one form of lookup table, and the total number
of table entries for UTC is smaller than for the other scales.
If the question simply wants "generic" UTC, then from the formal
definition we can only expect a precision of 1 millisecond. In that
case I could say "linear within the 1 ms precision of the formal
specification of UTC as defined by ITU-R TF.460", but according to
that as soon as a computer system clock deviates by more than 1 ms
it can no longer claim to be UTC. In that case what is it?
This is the vocabulary issue which triggers me to answer "mu", for
many of the questions seem to want an answer which is far simpler
than required to describe (or even in denial of) reality.
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
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