A timer is a kind of clock that uses a standard atomic resonance frequency (FIA) as a component in the maintenance time. They are far more accurate and occurrence rules identified, and used as primary standards for international services allocation of time to manage the regular television broadcasts, as well as in global navigation satellite and the GPS.
Automatic watches do not use radioactivity, other than the microwave signal with the specific intent of electrons in atoms emit when they transform energy level. Close to the atomic clocks are beginning to maser. Today, more precise atomic clocks located on the spectroscopy of fusion of atoms atomic spring frosts as the NIST-F1.