[LEAPSECS] Toasting Unix timestamp 1234567890

[Magnus Danielson]

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