On Thu, 10 Jul 2003, Steve Allen wrote:
> So we now have radio broadcasts with carriers and ticks in atomic
> seconds, and that is definitely much better than the clumsy attempts
> to match UTC with UT2 that preceded 1972. But there are almost no
> clocks on the planet which actually keep UTC. A UTC clock (and by
> extension of seconds into days, a UTC calendar) must have a table of
> all historic leap seconds, and warning about upcoming leap seconds.
> This is annoying at best, and impractical in most cases.
Indeed (as I've previously noted), UTC clocks seem fairly impossible to
acquire in any sort of size and cost of package that one would expect for
an "ordinary" clock (though the market of people wanting to watch a clock
tick 23:59:60 UTC would be fairly small). As far as I know clocks that
use radio time signals do not show 23:59:60 during a leap second if that
information is even available from the time signals (and many such clocks
use a dial that can't show 23:59:60 rather than a digital display anyway),
and consumer GPS receivers are reported as generally running slow on their
time display anyway and not showing leap seconds either. (I'd be glad to
be proved wrong; I've never got a manufacturer of consumer devices to
reply to enquiries (carefully referencing specific numbered subsections of
the specifications of the relevant signals) about how their devices
display leap seconds.) A UTC clock can be displayed on a computer that
specially processes leap second warnings from NTP, or is connected to
devices designed to receive (radio or GPS) time signals for precise time
synchronisation, but this is far off any sort of "ordinary" clock.
--
Joseph S. Myers
jsm28_at_cam.ac.uk
Received on Fri Jul 11 2003 - 03:08:51 PDT