The Rugby radio station, with call-sign GBR, was brought into service in 1926 by the Post Office as a telegraphy station with world-wide coverage and a frequency of 16 kHz. On 19 December 1927 it started carrying time signals from the Royal Observatory, 306 pulses in the five minutes up to and including the hours 10 and 18 GMT, with the six minutes pulses lengthened. These signals could be received throughout the world. The carrier frequency, although keyed by telegraphy traffic, was used as a frequency reference for many years, and its frequency was monitored and published by NPL. Its use as a reference became more difficult in 1967 when frequency-shift keying was introduced. GBR ceased to transmit time signals at the end of November 1986, and was relocated from Rugby at the end of March 2003. It is no longer used as a frequency reference. The MSF transmission was also relocated from Rugby, to Anthorn in Cumbria, on 31 March 2007.