[LEAPSECS] The relation between calendars and leap seconds.

[Steve Allen]

On Tue 2008-11-11T09:17:21 +0000, Poul-Henning Kamp hath writ:

>       The limited human intelligence.


I agree with the point, but I might qualify it better, as with the
tsunami response, to say: limited cognition of any given set of
individuals at any given point in their development, not an inherent
limit so much as one based on practical experience and teaching
and research.

But getting back to civil time that sort of limit produces these
two very disparate interpretations of what Hugo Chavez did in
Venezuela last year:

Venezuela's new time is officially with respect to the
Greenwich meridian
http://www.tsj.gov.ve/gaceta/noviembre/271107/271107-38819-01.html
and other documents make it explicit that the legal time is kept
by their naval observatory and that it is mean solar time.

The US DoS got the wording translated correctly
http://www.tsj.gov.ve/gaceta/noviembre/271107/271107-38819-01.html

But Denmark performed an interesting substitution
http://www.gkcaracas.um.dk/da/menu/Eksportraadgivning/Markedsmuligheder/Landeinformation/Time/

Whereas I'll admit this is likely one aspect of limited human
cognition -- the failure to recognize a significant difference
between UTC and GMT, with effort it could be interpreted to
say that Denmark expects that UTC and GMT will remain
indistinguishable.

Here's an interesting point.  Nobody misinterprets GPS time.
Nobody tries to extrapolate it backwards and make algorithms
about proleptic GPS time.  That's because GPS time simply
did not exist prior to 1980-01-06.  Nobody can screw it up
because GPS time is exactly and only what the US military
wants it to be.

But there are lots of examples of systems which try to assign meaning
to proleptic UTC, proleptic POSIX time, MS Windows time, .NET time, etc.
Proleptic interpretation of UTC is horribly broken with lots of
disagreeing algorithms even only for the late 20th century.

One of the best ways to limit the kinds of mistakes that limited
human cognition makes is to put the toys out of their reach.

I still assert that the safest means of going forward is for ITU-R to
wash their hands of UTC and say

    We don't care what you do with UTC, and we can't get the rest of
    the world to agree on whether or not UTC should change.  But we
    are sure that the machines of the world need a broadcast and
    internet time scale which increments predictably.  We're going to
    follow the advice of the Torino conference and call it Temps
    International (TI), and it will start being brodacast around 2022.
    If somebody wants to keep on maintaining UTC that's fine, but not
    us.

That is the sort of thing that is within the purview of the princes of
ITU-R.  Other princes will certainly keep on decreeing changes to the
civil time of various jurisdictions, and zoneinfo will handle that.
And if some other princes at BIPM and IERS want to maintain UTC with
leap seconds then they can do that, and zoneinfo can handle them too.
I hope BIPM and IERS will do that.

And if that happens then POSIX can make a very clear statment about
the interpretation of time_t.  They can just admit that the
interpretation before the UTC/TI cutover is a bit fuzzy, but point out
that the interpretation after the UTC/TI cutover is clearly defined.

One of the requirements of this process is to distinguish between
things that are not necessarily the same, between different things
that are only the same because of a convention created by ancestors
who had their own limited cognition.

Nothing requires that the broadcast/internet time scale be called UTC.
They are different things.  This was pointed out 5 years ago in Torino.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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