Zefram skrev:
Magnus Danielson wrote:
Sorry, I think you over-interpret a poorly articulated formulation of
mine. If you think according to "Honour the UTC definition from 1970 to
1972 and then the new leap-second based UTC definition from 1972 up to
current time" then I think you should come to the same conclusion as I
do.
I was thinking precisely in terms of using UTC in both eras, counting
UTC seconds. Thus I count UTC's leaps of both eras.
Zefram skrev:
The current offset is about 24.107757997 s, and does not have a terminating
decimal representation. (This is the counting-UTC-seconds way.)
I do not understand what that number comes from. Does not match what I
meant at least, so you need to describe what it means.
The 24 corresponds to the 24 positive leap seconds since 1972.
The remainder corresponds to pre-1972 leaps. In fact there is exactly
one such leap after the Unix epoch, and that is the final one at the
end of 1971 which brought UTC seconds into alignment with TAI seconds.
The duration of that leap was exactly 0.107758 TAI seconds. At the
then-prevailing rate of 1 UTC second = 1.00000003 TAI seconds, the
duration of the leap was exactly 10775800/100000003 UTC seconds, or
approximately 0.107757997 UTC seconds.
I gathered that eventually and it makes perfect sense. You only made a
very brief discussion over it so I did not get the right triggers. The
leap in TAI-UTC offset as measured in TAI seconds needs to be converted
into UTC seconds. However... is it the UTC seconds of the previous era
or the new era? It's a singularity so you can't use the slope of the
previous era, infact the scope of that era goes to but does not include
the UTC time of 1 Jan 1972 00:00:00, so the jump can not be included in
that era. So I think your calculation is actually wrong in this respect
and that 63072000.107758 UTC seconds is the time that has passed.
The number of elapsed UTC seconds from 1972-01-01T00:00:00 UTC to any
UTC midnight in 2009 is exactly 86400*(number of elapsed days) + 24 +
10775800/100000003.
I am starting to disagree about the last term there.
It seems clear to me, but I studied it quite closely to write the Perl
module Time::UTC (which is what I've used to extract some of these
numbers). I guess it's trickier than it looks.
It is tricky... I think you need to explain how you interpret the
range-definitions as I interpret them a little bit different.
It is a bit of a mess. Honouring the pre-1972 UTC definition for the
pre-1972 era makes sense as it allows for a practical solution at least,
as only integer offsets is involved.
...
it does not really help for the pre-1972 era where leap seconds was not
used,
You seem to think there were no leaps in UTC before 1972. Evidently
that's why you get confused about the fractional number of leap seconds.
No, I know there is leaps, but no leap seconds. There are several
fractional second leaps. I was only challangeing the wording to denote
"leap seconds" to fully disregard the shifts and ramps there is.
At 1 Jan 1972 we jumped from 9,892242 to 10 s offset in one fractional
step.
But this is a reference to the irregular leap.
Yes, but you confuse my separation of leaps with leaps though the use of
the leap second mechanism in which you jump integer seconds.
Before that we had a 3E-8 s/s phase ramp from 8,000082 of 1 Jan
1970. Neither qualify as leap seconds.
The frequency offset isn't a leap, because it doesn't give UTC days an
irregular number of UTC seconds. But the 1971-12-31 leap, and earlier
leaps that were mostly of 0.1 TAI seconds, certainly are (fractional)
leap seconds.
Which is also what I wanted to say. When going back to
1970-01-01T00:00:00Z and then counting from that, just disregarding leap
seconds only helps us back to what happend since 1972-01-01T00:00:00Z
since only since then the leap seconds have been used as an adjustment
mechanism. Previous to that a combination of time and frequency offsets
was used, but I do not call them leap seconds...
Also, the leap was on 1972-01-01T00:00:00, which is why it should not be
included in the 30 ppb frequency era.
When I first read about the rubber seconds era, I got the impression
that it was done solely by frequency offsets, with no leaps. How much
easier would our lives have been if that were the case?
Much.
Cheers,
Magnus
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