To get round this problem they came up with a new time scale which used the seconds of atomic time but which added or subtracted seconds to keep it in step with the earth's natural time. It is the International Earth Rotation Service in Paris which measures the rotation of the earth and determines when a leap second is needed. Atomic time and UTC are kept through the collaboration of about forty laboratories worldwide, each having several atomic clocks. NPL broadcasts time signals from a transmitter at Rugby. Anyone with a suitable receiver can set their clock directly against the national atomic clock.
Some domestic clocks are now available with an in-built receiver.
As mentioned earlier, we take accurate timekeeping for granted. Our present technology-based society would collapse without very accurate clocks. Even the most unpunctual person will be dependent on the timekeeping provided by an atomic clock when making a phone call, since these clocks control the effective operation of national and international telecommunications networks. In another critical application, radio signals from atomic clocks situated in satellites enable ships equipped with special receivers to locate their position to a few tens of metres. So trade and commerce are dependent on accurate timekeeping today just as they were a few hundred years ago.