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The wording of the definition of the meter has apparently changed recently. I'm wondering about the motivation for the change. The current definition is:

The older definition (1983, I think) wasThe meter, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuumcto be 299 792 458 when expressed in the unit m s-1, where the second is defined in terms of ΔνCs.

Does anyone know when and why the change was made?Themetreisdefinedas the length of the path travelled by light in a vacuum in 1299 792 458 of a second. .

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