Atomic clock

An atomic clock is a type of clock so as to uses an atomic resonance frequency standard as its counter. Early atomic clocks were masers by means of attached equipment. Today's best atomic frequency standards (or clocks) are based on more advanced physics involving cold atoms and atomic fountains. National standards agencies maintain an accuracy of 10-9 seconds per day, and a precision equal to the frequency of the radio transmitter pumping the maser. The clocks keep up a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but coordinated with the passing of day and night based on astronomical observations.