International Atomic Time (TAI)

Acronym: TAI
In French: Temps Atomique International

TAI is an international time standard. It is calculated by the BIPM from the readings of more than 200 atomic clocks located in metrology institutes and observatories in more than 30 countries around the world.

TAI's unit interval is exactly one SI second at mean sea level. The origin of TAI is such that UT1-TAI was approximately 0 on 1 January 1958.

BIPM estimates that TAI does not lose or gain with respect to an imaginary perfect clock by more than about one tenth of a microsecond (0.0000001 second) per year.

TAI is a continuous time scale which is not connected to Earth rotation. UTC is derived from TAI by introducing leap seconds.

Related terms:

• Coordinated Universal Time
• leap second
• Universal Time (UT1)

Related links:

• Bureau International des Poids et Mesures (BIPM)
• International Atomic Time (BIPM information)