Resolution 9 of the 11th CGPM

Definition of the unit of time (second)

The 11th Conférence Générale des Poids et Mesures (CGPM),


  • the powers given to the Comité International des Poids et Mesures (CIPM) by the 10th CGPM to define the fundamental unit of time,
  • the decision taken by the CIPM in 1956,

ratifies the following definition:

"The second is the fraction 1/31 556 925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time."

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


This definition was abrogated in 1967 by the 13th CGPM (Resolution 1).

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