[LEAPSECS] a modest proposal
sla at ucolick.org
Sat Feb 9 23:36:02 EST 2008
What if the plan outlined at Torino in May 2003 were to be
implemented, but with a few more details?
I think the resolutions from Torino do need a little more detailed
guidance about implementation by various systems, and chief among
those is the interaction with POSIX.
I think that the ITU-R is not well structured to be in charge of
defining a time scale. It is good for defining radio broadcasts. I
think that the ITU-R should retire TF.460, and at the same time adopt
a new resolution as called for in Torino, defining International Time
(TI). Radio broadcasts of precision time signals should give TI.
I think that POSIX time_t should be redefined to be TI, with no leap
seconds. I think that the leap seconds should be included in the
zoneinfo files. POSIX already allows that the local time can be
offset by an arbitrary number of seconds (not just hours and minutes)
from the system value of time_t. The mechanism by which this is
communicated to POSIX systems is zoneinfo. The zoneinfo maintainers
are accustomed to making changes many times a year, with almost no
advance notice, subject to whims of political entities which are
much less predictable than leap seconds.
This keeps the simplicity of POSIX system time with the only cost
being one of interpretation: the system time_t is TI, and UTC be an
entity derived using zoneinfo.
I think the ITU-R should formally turn UTC over to the BIPM, to be
maintained in conjunction with the IERS. This makes UTC a two-agency
activity rather than the current three agencies.
This allows BIPM to maintain full authority over all time scales,
precision and civil.
This allows all the bureaus of the IERS to continue to represent to
their funding agencies that their work is essential for the purposes
of telling the world what time it is. (If UTC were redefined instead
of replace with TI, the earth rotation monitoring of the IERS becomes
moot from the standpoint of commerce.)
It seems to me that with these changes in effect
*almost nothing technical breaks*!
Yes, at a bureaucratic and political level they are major upheavals
and they require serious cooperation between many agencies.
They require NIST and other national time bureaus to make the case
that it is internationally desirable to broadcast a time scale which
has a slightly more complicated relationship to the legal civil time
than it used to have.
But at a technical level all the mechanisms already exist and work.
The worst effect I see is that maintaining the zoneinfo files becomes
a tad trickier.
There are very few systems which are not POSIX compliant, and not
capable of updating their zoneinfo.
I recognize that a few things do break, chief among them the radio
controlled clocks and wristwatches which currently give correct civil
time. Nevertheless, I assert that for non-civil purposes it is merely
a bureaucratic change to have to note that, e.g., the radio-controlled
timestamps on the milk cartons are now actually TI instead of UTC.
For those radio-controlled clocks which must give correct civil time,
I assert that they will pass unobtrusively into obsolescence or be
upgraded before the difference between UTC and TI becomes relevant.
The worst case will be those WWVB clocks (and similar longwave systems
in other regions) which are digital, for they will show the missing
leap seconds clearly. (I discount the analog versions from the start,
for the three mechanical WWVB clocks that I brought back from my dad's
place have already stripped the gears for their second hands.)
I am also prepared disregard the recommended date from Torino. If
done well there is no need to wait until year 2022.
I can't remember whether LEAPSECS has discussed this particular way
of implementing the change, but I think it has not been so.
The question then is
What objections are there to this way of getting leap seconds out of
broadcast time signals while keeping them in UTC?
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855
University of California Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
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