Re: [LEAPSECS] Wall Street Journal Article

From: Poul-Henning Kamp <>
Date: Sun, 31 Jul 2005 09:19:40 +0200

In message <>, Steve Allen writes:
>On Sun 2005-07-31T08:23:30 +0200, Poul-Henning Kamp hath writ:
>> No, they had everything to do with computers don't liking time to
>> jump around.
>But the reality is that no computer system (or any system, for even
>NIST and USNO don't know what the value of TAI and UTC is until next
>month) can guarantee that it always knows what time it is.

Non sequitur.

The topic is: why do IT installations and manufacturers not test
leap-seconds. The answer is: because it costs too much.

>> When you start out on a long march, you don't put a stone in your
>> boot deliberately, and if one is there already, you take it out.
>> Leapseconds is such a stone for real-world IT installations.
>In this sense leap seconds give the system designer the opportunity
>and incentive to face reality instead of ignoring it. Taking away
>leap seconds will not fix this.

We're all entitled to our own realities. Yours seem to not coincide
with the IT industry to any great extent.

>> I'm pointing out that UTC with leap seconds is unsafe at any speed.
>Presuming that the system clock is always right is delusional.

Non sequitur again.

>> It would have been much smarter to use TAI, wouldn't it ? I thought
>> I heard some astronomer say in this discussion that all applications
>> which need proper timekeeping should use TAI ?
>If "proper timekeeping" means time as defined by physics then:
>All applications which need proper timekeeping in the reference frame
>of the solar system should use TCB.
>All applications which need proper timekeeping in the terrestrial
>environment should use TCG.
>All applications which need proper timekeeping on the surface of the
>earth should use TT.
>These are the recommendations from astronomers to everyone.
>But these are not practical time scales. [...]

So why would astronomers be recommending them ?

>> And if anything, if astronomers switched to TAI on 2008-01-01 they
>> would not run into this problem in the future.
>TAI is a practical time scale, but its seconds are not of constant
>length. [...]

Considering that we're comparing to a timescale which would be
off by an hour in 600 years, I think these effects can be ignored
for now and astronomy could use TAI profitably.

>> I think the sneakage happened in 1972 and we're trying to evict it.
>Leap seconds were proposed and instituted by the physicists who ran
>the atomic clocks. They were opposed by many astronomers, but after
>the shouting stopped (and in the proceedings of the IAU GAs it is
>evident that there was shouting) the astronomers agreed that UTC as SI
>seconds with leap seconds was the best option.

But let me turn this around for a second:

I don't hear the counter proposal from the astronomers to fix leap

I hear whinage about leap hours (which might or might not happen,
depending on what scientists in the next 500 years decide) but I
don't hear anything about how to fix UTC when leapseconds no longer
are able to cope with the rate of DUT1 change.

Is this discussion really just about astronomers trying to make
sure this doesn't happen in their lifetime, and if not, why are
there no counter proposals for a better solution ?

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk_at_FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Received on Sun Jul 31 2005 - 00:19:59 PDT

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