It is the basis for Coordinated Universal Time (UTC), which is used for civil timekeeping all over the Earth's surface and which has leap seconds.
In 2022, the General Conference on Weights and Measures decided to abandon the leap second by or before 2035, at which point the difference between TAI and UTC will remain fixed.
[5] TAI may be reported using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth.
TAI in this form was synchronised with Universal Time at the beginning of 1958, and the two have drifted apart ever since, due primarily to the slowing rotation of the Earth.
The participating institutions each broadcast, in real time, a frequency signal with timecodes, which is their estimate of TAI.
Time codes are usually published in the form of UTC, which differs from TAI by a well-known integer number of seconds.
The latter is not to be confused with TA(NPL), which denotes an independent atomic time scale, not synchronised to TAI or to anything else.
In hindsight, it is possible to discover errors in TAI and to make better estimates of the true proper time scale.
From its beginning in 1961 through December 1971, the adjustments were made regularly in fractional leap seconds so that UTC approximated UT2.
The less frequent whole-second adjustments meant that the time scale would be more stable and easier to synchronize internationally.