how accurate is gmt

[mjandrews96]

following on from peppy's question about z time i have noticed the gmt time signal is different on my normal radio and my dab radio also sat tv they all arrive at different times why is this and why do we still use gmt if uct (atomic time) is accurate to 1-sec every thousand years

[kempie]

In modern practice we don't "use" GMT even if people call it by that name, but old habits die hard and because there is so little difference between GMT and UTC people tend to use the two terms interchangeably.

All digital signals received by DAB radios or satellite boxes require a finite amount of time to be coded and decoded. This is the cause of the apparent time delay when compared to terrestrial TV/Radio signals.

[heathfield]

Back in the days of 'the wireless' it was aknowledged that there could be anything up to a 10 second delay between actual GMT and listeners hearing the time signal.

[chakka35]

Time pips are no longer distributed centrally from Greenwich to every broadcaster. Many companies generate their own pips. Even then delays due to the time to travel to and from a satellite introduces a delay. (I used to watch the Proms on my television while listening to the sound on Radio 3 but they are no longer in sync because one comes by landline and the other by satellite.)
The best thing is to buy a radio clock (controlled by long wave from Rugby) which is accurate to within one second in a million years. That way you can check on all the pips (and Big Ben) and jeer when they get it wrong.