High Quality Content by WIKIPEDIA articles! International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth`s geoid. It is the basis for Coordinated Universal Time (UTC), which is used for civil timekeeping all over the Earth`s surface, and for Terrestrial Time, which is used for astronomical calculations. Since 2008-12-31 when the last leap second was added, TAI has been exactly 34 seconds ahead of UTC. This is still true as of 2011-09-01. 34 seconds results from the initial difference of 10 seconds at the start of 1972, plus 24 leap seconds in UTC since 1972.