Radio Controlled Technology
The clever bit is that these clocks check the radio signal with the MSF signal transmitted from Cumbria which is accurate to 1000ths of a second a year. It regularly compares the time with the signal, correcting itself if necessary and automatically changes when the clocks go back in Autumn or forward in Spring.
Some manufacturers refer to their radio controlled clocks as "atomic clocks", this isn’t really true. An atomic clock works from a cesium or rubidium oscillator, where as a radio controlled clock receives a radio signal transmitted from an atomic clock.
MSF Radio Time Signal
An MSF signal is transmitted in the UK from Anthorn Radio Station in Cumbria by VT Communications, under contract to the NPL (National Physics Laboratory) and provides a reliable and accurate time signal omnidirectinal across the whole country and can even be received in Northern Europe. The signal can be decoded by the receiver found in radio controlled clocks and converted in to a time and date display.
The MSF signal includes:-
day of month
day of week
British Summer Time (in effect or imminent)