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The BIPM (Bureau International de Poids et Mesures) defines the meter as the distance traveled by light in $\frac{1}{299792458}$ seconds. The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. The speed of light as $299792458$ m/s is therefore exact and not a measured value. Similarily, ...


This is an exact value. Meter is defined by the speed of light. Meter is a distance that the light travels during $\frac{1}{299792458}$ of a second.

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