Accurate Length Measurement of Meter Bar with Helium-Neon Laser

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Science  25 Dec 1964:
Vol. 146, Issue 3652, pp. 1672-1673
DOI: 10.1126/science.146.3652.1672


A helium-neon gas laser has been successfully used in conjunction with an automatic fringe-counting interferometer to measure the length of a meter bar. The agreement obtained was 7 parts in 100 million with respect to the assigned length of the bar.