Clive D.W. Feather <clive@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. http://www.timesonline.co.uk/tol/news/uk/article5425798.ece 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 river). Any others? Tony. -- f.anthony.n.finch <dot@dotat.at> http://dotat.at/ North Utsire: Northerly or northwesterly 5 to 7, decreasing 4 later. Moderate or rough. Occasional rain. Moderate or good.