Resolution 1 of the 14th CGPM (1971)

International Atomic Time, function of CIPM

The 14th Conférence Générale des Poids et Mesures (CGPM),


  • that the second, unit of time of the Système International d'Unités, has since 1967 been defined in terms of a natural atomic frequency, and no longer in terms of the time scales provided by astronomical motions,
  • that the need for an International Atomic Time (TAI) scale is a consequence of the atomic definition of the second,
  • that several international organizations have ensured and are still successfully ensuring the establishment of the time scales based on astronomical motions, particularly thanks to the permanent services of the Bureau International de l'Heure (BIH),
  • that the BIH has started to establish an atomic time scale of recognized quality and proven usefulness,
  • that the atomic frequency standards for realizing the second have been considered and must continue to be considered by the Comité International des Poids et Mesures (CIPM) helped by a Consultative Committee, and that the unit interval of the International Atomic Time scale must be the second realized according to its atomic definition,
  • that all the competent international scientific organizations and the national laboratories active in this field have expressed the wish that the CIPM and the CGPM should give a definition of International Atomic Time, and should contribute to the establishment of the International Atomic Time scale,
  • that the usefulness of International Atomic Time entails close coordination with the time scales based on astronomical motions,

requests the CIPM

  1. to give a definition of International Atomic Time,
  2. to take the necessary steps, in agreement with the international organizations concerned, to ensure that available scientific competence and existing facilities are used in the best possible way to realize the International Atomic Time scale and to satisfy the requirements of users of International Atomic Time.

DOI : 10.59161/CGPM1971RES1E

The reader should note that the official version of this Resolution is the French text


The definition of TAI was given by the CCDS in 1970 (now the CCTF).

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