Re: Calabretta's 86400 s + epsilon day proposal

From: Markus Kuhn <>
Date: Thu, 30 Jan 2003 15:39:26 +0000

Mark Calabretta wrote on 2003-01-30 00:58 UTC:
> I note that, as yet, we have not heard a reasoned argument against my
> proposal for UTC to measure the true length of day in SI seconds.

If you make every UTC day 86400 + epsilon(date) days long, then life
gets more difficult for people who broadcast standard frequencies such
as 50.00000000 Hz TV sync signals, because now you can't simply say that
you start a new TV frame exactly at the start of a new second (with UTC
you can, even across leap second!). Note that the vast majority of
critical frequencies we have are an integer number of hertz. It is very
convenient to adjust these by triggering an oscilloscope from the 1
pulse-per-second output of an atomic clock or time signal receiver and
then observe the phase wander of your oscillator. Such adjustments would
break down if UTC clocks would start to have now 1 pulse-per-(something
that is an SI second most of the time).

The technical importance of pulse-per-second and integer-Hertz signals
was a strong reason for why we moved from smooth UTC to leap-second-UTC
in 1972, and your proposal would reverse that improvement. That's why I
don't like it.

Even if, a procedure would still have to be put into place to define the
function epsilon(date). How long in advance would IERS have to announce
this function?

If I understood you correctly, all you propose is to replace the full
leap second at the end of a day every few years by a couple of leap
microseconds at the end of the every UTC day, right? That sounds
slightly more complicated to me and doesn't fundamentally eliminate the
problem that there still will exist UTC time stamps after 23:59:59.9999999...

You could alternatively stretch the length of the UTC second at the end
of each day, and this way your proposal would be similar to UTS, except
that you make the correction every day whereas I prefer to limit it to
the vicinity of each current UTC leap second. But pulse-per-second
signals would experience a phase jump at the end of every day ... :-(


Markus Kuhn, Computer Lab, Univ of Cambridge, GB | __oo_O..O_oo__
Received on Thu Jan 30 2003 - 07:39:36 PST

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