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metre

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The metre is the length equal to $1\,650\,763.73$ wavelengths in vacuum of the radiation corresponding to the transition between the levels $2\rm{p}^{10}$ and $5\rm{d}^{5}$ of the krypton 86 atom.

This definition is valid from 1960-10-14 to 1983-10-16
Unit metre
Symbol m
Quantity length
Defining Resolution
CGPM Resolution 6 (1960)
Unit Type SI base unit
Notes:
  1. The old international prototype of the metre which was sanctioned by the 1st CGPM in 1889 is still kept at the BIPM under the conditions specified in 1889.
www.bipm.org