The signal's carrier frequency is maintained at 60 kHz to within 2 parts in 1012, controlled by caesium atomic clocks at the radio station.

From 19 December 1927, it broadcast a 15.8 kHz time signal from the Royal Observatory which could be received worldwide.

[5] Eventually, time signals from GBR were terminated in November 1986 and it is no longer used as a frequency reference.

The 60 kHz signal finally became an uninterrupted 24-hour service in 1966, and the frequency references were discontinued in February 1988.

[9] The formal inauguration of the relocated facility took place on 1 April 2007, when the name of the service became "The Time from NPL" and the signal from Rugby was permanently switched off.

[citation needed] Currently, the signal from Anthorn is still useable, in the location of the Mediterranean, although it is weaker than Rugby.

[6] The official history of the service says that "Rugby was given an additional commitment for the transmission of reference Modulated Standard Frequencies", but no actual explanation is given for the call sign "MSF".

[14] According to the NPL it seems the call sign was chosen so that it could be memorized as "Master Standard Frequency" but MSF was not intended to be an abbreviation.

[15] The transmitted signal has an effective radiated power of 17 kW, on a frequency of 60 kHz to within 2 parts in 1012.

The vertical part of the antenna radiated the signal, so that the received strength was similar in all directions (it was approximately omnidirectional).

[6] In addition to professional uses where accurate time is required, radio-controlled clocks (including wristwatches) with both digital and analog displays using the NPL signal are widely used.

The rise and fall times of the 60 kHz carrier are determined by the combination of antenna and transmitter.

However the official NPL documentation states that these “fixed value bits” 01A-16A, 17B-51B, and 52B and 59B are currently set at '0', but that they may be used in the future.

MSF does not broadcast any explicit advance warning of upcoming leap seconds, which occur less than once a year on average.

[3] The only indication is a change in the number of padding bits before the time code during the minute before the leap second.