A Jurghans Mega 1 radio-controlled wrist watch, seen next to an 18th century pendulum clock. The watch picks up radio time signals from the atomic time relay station near Frankfurt, Germany. When within a radius of 1,500km from Frankfurt, the watch keeps time precisely in line with the CS2 caesium atomic clock, the most accurate caesium clock in the world. Outside of this radius, the watch uses conventional circuits to keep time, automatically readjusting when contact is regained with Frankfurt. Part of the watch strap has been removed to reveal the radio aerial.