Recommendation 1 of the 24th CCEM (2005)

On the possible redefinition of the kilogram

The Consultative Committee for Electricity and Magnetism (CCEM),


  • the recent proposal to redefine the kilogram in terms of a fixed value for either the Planck constant or the Avogadro constant at the 23rd General Conference in 2007,
  • that the realization of a definition of the kilogram in these terms necessarily requires the permanent availability of experiments that relate mass to fundamental constants,
  • the advantages that such a redefinition would bring to the scientific community through the significant reduction in the uncertainties of the SI values of many fundamental constants,
  • that a redefinition with a fixed value for the Planck constant, if combined with a redefinition of the ampere fixing the value of the elementary charge, would have further benefits for the scientific community, particularly in electrical metrology,

recalling Resolution 7 of the 21st General Conference (1999), which recommended that national laboratories continue their efforts to refine experiments that link the unit of mass to fundamental or atomic constants with a view to a future redefinition of the kilogram,


  • the existing discrepancy of about 1 part in 106 between the results from watt balance and x-ray crystal density measurements,
  • the fact that this discrepancy is significant at the practical level and is unlikely to be resolved by 2007,

recommends that

  • any decision on redefining the kilogram be deferred until the 24th General Conference in 2011,
  • laboratories continue to make their best efforts to produce data for the 2010 CODATA adjustment of the values of the fundamental constants to support a possible redefinition of the kilogram at the 24th General Conference,
  • at that time, consideration be given to fixing the values of both the Planck constant and the elementary charge.

DOI : 10.59161/CCEM2005REC1E

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

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