Resolution 5 of the 12th CGPM (1964)

Atomic standard of frequency

The 12th Conférence Générale des Poids et Mesures (CGPM),


  • that the 11th CGPM noted in its Resolution 10 the urgency, in the interests of accurate metrology, of adopting an atomic or molecular standard of time interval,
  • that, in spite of the results already obtained with caesium atomic frequency standards, the time has not yet come for the CGPM to adopt a new definition of the second, base unit of the Système International d'Unités, because of the new and considerable improvements likely to be obtained from work now in progress,

considering also that it is not desirable to wait any longer before time measurements in physics are based on atomic or molecular frequency standards,

empowers the Comité International des Poids et Mesures to name the atomic or molecular frequency standards to be employed for the time being,

requests the organizations and laboratories knowledgeable in this field to pursue work connected with a new definition of the second.

DOI : 10.59161/CGPM1964RES5E

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

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