Recommendation 1 of the 11th CCQM (2005)

On the possible redefinition of the kilogram

The Consultative Committee for Amount of Substance: metrology in chemistry (CCQM),

considering

• 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 measurement techniques that relate mass measurements 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 based on a fixed value for the Avogadro constant would have further benefits for the scientific community, particularly for metrology in chemistry,

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,

noting

• the existing discrepancy of about 1 part in 10⁶ between the results from watt balance and x-ray crystal density/molar mass 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, and should be based on consultation with all users and stakeholders that would be affected,
• laboratories continue to make their best efforts to produce data for the 2010 CODATA adjustment of the values of the fundamental constants in order to support a possible redefinition of the kilogram at the 24th General Conference,
• at that time, full consideration be given to fixing the values of either the Planck constant or the Avogadro constant, and the interests of the chemical metrology community in this choice,
• any new definition of the kilogram should, if possible, be easily understood by the general public.

DOI : 10.59161/CCQM2005REC1E