Resolution 8 of the 22nd CGPM

Revision of the mise en pratique of the definition of the metre

The 22nd General Conference,

recalling that

  • the 21st General Conference in 1999 welcomed the adoption in 1997 by the International Committee of a revised mise en pratique of the definition of the metre, and
  • the Conference also recommended that national laboratories pursue experimental and theoretical research on optical wavelength and frequency standards, including the development of new techniques for the comparison of different standards over a wide range of wavelength and frequency to improve yet further the experimental basis of the International System of Units (SI),

considering that

  • new techniques based on trapped ions and atoms have opened up the possibility of highly accurate and stable optical clocks and frequency standards,
  • these systems appear to have the potential for providing the basis for a future, improved, definition of the second,
  • the introduction of femtosecond comb technology has considerably facilitated the absolute frequency measurement of optical radiation sources, including those sources used to realize the metre,
  • the International Committee in 2002 updated the recommended values of a number of radiations published in the 1997 mise en pratique and added values for several new radiations,


  • the adoption of these new values and their subsequent publication in Metrologia in 2003, and
  • the close collaboration and discussions between the length and time and frequency communities aimed at the eventual linking of optical and microwave frequency standards,

recommends that national laboratories continue to develop reliable and proven techniques for the generation and comparison of optical and microwave frequency standards, and

invites the International Committee to keep this important subject under regular review, especially in relation to a possible redefinition of the second.

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

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