Editing Greenwich Time Signal (section)

==Accuracy==
The pips for national radio stations and some local radio stations are timed relative to [[UTC]], from an [[atomic clock]] in the basement of [[Broadcasting House]] synchronised with the [[National Physical Laboratory, UK|National Physical Laboratory]]'s [[Time from NPL]] and [[GPS]]. On other stations, the pips are generated locally from a [[GPS]]-synchronised clock. The broadcast pips usefulness for time [[calibration]] is diminished by the time lags involved in digital broadcasting.

The BBC compensates for the time delay in both broadcasting and receiving equipment, as well as the time for the actual transmission. The pips are timed so that they are accurately received on [[long wave]] as far as {{convert|160|km|-1}} from the [[Droitwich AM transmitter]], which is the distance to [[Central London]].

As a pre-digital time transfer and transmission system, the pips have been a great technological success. In modern times, however, time can be transferred using [[IRIG timecode|IRIG]] and pre-[[Network Time Protocol|NTP]].

Newer digital broadcasting methods have introduced even greater problems for the accuracy of use of the pips. On digital platforms such as [[Digital Video Broadcasting|DVB]], [[digital audio broadcasting|DAB]], satellite and the [[Internet]], the pips — although generated accurately — are not heard by the listener exactly on the hour. The [[codec|encoding and decoding]] of the digital signal causes a delay, of usually between two and eight seconds. In the case of satellite broadcasting, the [[Time of arrival|travel time]] of the signal to and from the satellite adds about another 0.25&nbsp;seconds.