This wall clock is so good we have put our name on it its secret is that it picks up the official british standard frequency time signal broadcast by the bt international transmitter at cumbria effective up to a radius of 1500km 932 miles and accurate to 1 second in 60 million years our clock calibrates itself every two hours against this time signal making it one of the most accurate clocks in the world you can check it to the second against the speaking clock or the bbcs pips it even