international atomic time (TAI)

The time reference of the international atomic time (TAI) is based on the constancy of atomic clocks using the radiation of caesium atoms as a reference.

To calculate the international atomic time, data from 200 atomic frequency standards from 50 countries are compared. From these data, the Bureau International des Poids et Measures( BIPM) calculates the time. The International Atomic Time (TAI) is valid worldwide, it is extremely constant and serves as a reference for the Coordinated Universal Time( UTC).