[LEAPSECS] Metrologia on time

[cook michael]

Le 04/08/2011 07:27, Tom Van Baak a écrit :

> The question is -- does anyone use this any more? I'd guess

> that any person or any system that needs DUT1 has long since

> switched over to telephone, fax, or the internet to obtain this

> information. The last LF or SW radio that decoded DUT1 was

> made decades ago.

>

What must be clear now is that the currently transmitted resolution of 
DUT1 is not  much use for anything  except for a long range warning that 
a leap may be coming. I have seen references that a couple of Russian 
transmitters are or were transmitting DUT1 to 0,1s and a dUT1 to 0,02s 
resolution, so when they were installed I guess someone was interested 
in a better transmitted value. I agree that it is not clear that anyone 
is using it now.

> The internet is faster, more reliable, and far more global than

> LF or short-wave timecodes ever were. Further, you now get

> 4 or 5 digits of precision instead of just 1, as well as history

> and predictions tens or hundreds of days in advance. All with

> one line of code and a URL.

Hmm. I agree with the principle, but the historical data is not in a 
standard format and is not scaled uniformly so it needs more than one 
line of code to make it usable.


>

> After that issue is settled, then permitting DUT1 to temporarily

> spill over 1.0 seconds is the next hurdle.

Though I have no particular love for leap seconds, but  there is logic 
in ITU-R TF.460-6 at least for me, as it provides for the minimum 
requirements for any time transmission.
a) Ticks of SI seconds, used by all. Even though UTC is not uniform, the 
actual tick is on a TAI sec boundary +/-  a few nano seconds.
b) Current value for DUT1.  Possibly superfluous as c) is available on air.
c) A civil time scale, UTC, used world wide as a legal time scale, 
directly descending from and now synonymous with GMT and approximating 
to UT1 which is still the legal definition in many countries laws such  
that "day" has its traditional meaning.
d) All that available in one place if everyone plays ball.

The American (just happens to be them) proposition to modify  460-6 only 
takes account of a) , not coherently addressing any of the others and in 
fact positively discriminating against them, not even deigning to 
recommend the transmission of the difference between new UTC and UT1.  
New DUT1 will only be available from IERS. Not only that, but it is just 
assumed that that data will be "made available" in a uniform format and 
machine readable manner.  That means that anyone wanting to keep time 
with respect to generally understood notion of day has to get on the 
internet download the tables maintained in an ad hoc and voluntary  
basis and make the change, hoping of course that the scaling used hasn't 
changed by magic between one access and the next.  I hope their paper is 
flushed down an ITU-R toilet with due ceremony.  (end of rant)

I do like agree with most here that the transmitted time scale should be 
uniform and quite like Steve Allen's proposition, though there are as he 
freely admits issues to be taken care of. But I think that really  ITU-R 
WP7A should be packed off to a large padded cell and not let out until 
they have a formal proposition covering points a-d above.