dot at dotat.at
Fri Jul 1 17:55:47 UTC 2011
Clive D.W. Feather <clive at davros.org> wrote:
> Tony Finch said:
> >> Just to make things more complicated, civil time in the UK is GMT
> >> (approximately UT1) and *not* UTC. So clocks should never have 23:59:60.
> > De jure yes, but it is de facto UTC. GMT hasn't been maintained for
> > decades and almost all the UK government-sponsored time signals provide
> > UTC without DUT1.
> MSF provides DUT1.
As far as I know it's the only one that does. The NPL's other time
services all provide UTC(NPL) - telephone time service, Internet time
service (i.e. NTP), GPS common-view time transfer; The BBC broadcasts UTC
by phase modulation of the Droitwich 198kHz transmissions, and the Radio 4
pips are UTC from GPS.
According to this article, Big Ben is set from the speaking clock.
AFAIK the speaking clock doesn't have much in the way of precision
guarantees, though according to Wikipedia it also provides UTC. The NPL
FAQ on the subject has been deleted but Google's cached copy says:
The telephone 'speaking clock', the 'Timeline' service provided by BT
with sponsorship from Accurist, gets its seconds markers from an
accurate source of time. Even allowing for the delay in the telephone
network, you can probably expect the starts of the seconds pips to be
accurate seconds markers within about one-tenth of a second.
However, the labelling of these seconds is not controlled by, neither is
it monitored by, the NPL. If the 'speaking clock' appears to be
out-of-step with other time signals it would be appropriate to take the
matter up with BT.
The Government's short-lived "Greenwich Electronic Time" marketing
initiative incluses an atomic clock and NTP servers providing UTC from
Telehouse (which, as well as being a key Internet hub, happens to be
almost directly north of the Airy transit circle on the other side of the
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