[LEAPSECS] how bad precision timekeeping was
sla at ucolick.org
Tue Feb 12 21:38:06 EST 2008
I've got a lot of documents from the 1960s which indicate what was
going on with precise time. I've got a lot of retrospectives about
who did what. Many of these documents I can't just put on the web.
Even if they were on the web they require translation or footnoting
because they use jargon which was still in development and which has
since been discarded.
There is one public document which presents the picture in pretty
plain language. It was developed for NASA by a geodecist who had to
sit down with Markowitz in order to get the picture and then write
it all down in a way that folks not in the time bureaus could grok.
See the amount of effort that went into producing precise time,
and in changing the published conventional longitudes of every
time observing station on earth. See the amount of effort that
went into decoding broadcast signals in order to figure out
their meaning and make use of them for any precision purpose.
That horror is what the CCIR was fixing when they adopted UTC with
leap seconds, which they did unilaterally despite calls for discussion
by a handful of international scientific organizations. And that
document dates from before there was cesium at all the transmitter
locations for LORAN-C (imagine what it was like on New Years Eve when
entire chains of LORAN-C had to have techs on duty to implement time
steps along with carrier frequency and modulation shifts).
There are other documents from the 1970s which indicate significant
dissatisfaction with the new scheme of UTC, and with the way the CCIR
mandated it. (My impression is that the discussions in hallways and
at dinner parties were very interesting at the conferences with people
who were members of both CCIR and the committees of the various
On Tue 2008-02-12T20:13:47 +0000, Poul-Henning Kamp hath writ:
> I have only one thing against leap-seconds: they don't work in
> practice because the six month warning is an order of magnitude
> to short.
We have ample experience that nobody can tell the legislators and
bureaucrats not to mess around with summer/daylight time transition
dates, so we all have to deal with regular updates to the zoneinfo
mechanisms if we want our systems to produce the legal civil time.
If we move the leap seconds into that same mechanism we allow the
underlying broadcast and computer time scales to become uniformly
monotonic. Daniel Gambis always gives more notice to the whole world
than Hugo Chavez did to Venezuela last year.
> So we can save the expense of handling leap-seconds in software
> entirely by dropping leapseconds.
We have to resign ourselves to the expense of updating zoneinfo,
or the equivalents in Windows, and cell-phone towers, and anything
else that uses precision time and purports to supply civil time too.
Zoneinfo in its POSIX implementation includes enough ability to
handle the leap seconds.
Yes, most actions by the ITU-R have costs to various parties.
Despite the dissatisfaction, what the CCIR did in 1970 was a compromise.
We have the mechanisms in place to support a compromise.
Dropping leap seconds entirely would not be a compromise.
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855
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Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
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