## 13.6.3.2 TAI

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TAI (International atomic time) is a 'paper' clock in the sense that it is a computed average of lots of real, atomic clocks located all over the world.

TAI counts seconds, minutes, and hours as regularly as possible. Each TAI day has 24 TAI hours, each TAI hour has 60 TAI minutes, and each TAI minute has 60 TAI seconds. Each TAI second is, as closely as possible, one SI second. An SI second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

TAI time is independent of the rotation of planet Earth.

In Logiweb, TAI hour hh, minute mm, and second ss is written TAI:hh:mm:ss. We have 00 <= hh <= 23, 00 <= mm < 59, and 00 <= ss <= 59. Occasionally, we shall use TAI:24:00:00 to denote TAI:00:00:00 on the following day. Decimal fractions of a second are written after a dot as in TAI:12:23:34.456 which denotes 0.456 seconds past TAI:12:23:34. The notation is compatible with ISO 8601 except that we prepend 'TAI:' to emphasize the use of International Atomic Time.

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Copyright © 2010
Klaus Grue,
GRD-2010-01-05