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Length of a Meter 1983

How was the length of a standard meter redefined in the year 1983?

On October 20, the meter was redefined again. The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is

c = 299,792,458 m/s

The second is determined to an uncertainty, U = 1 part in 1014 by the Cesium clock. The General Conference made the iodine stabilized Helium-Neon laser a recommended radiation for realizing the meter at this time. The wavelength of this laser is

λHeNe = 632.99139822 nm

with an estimated relative standard uncertainty (U) of ± 2.5 x 10−11.

In all of these changes in definition, the goal was not only to improve the precision of the definition, but also to change its actual length as little as possible.