The base unit of length in the SI system . Historically, the meter has been defined in numerous ways. It has been defined as 1/10,000,000 of the quadrant of the Earth's circumference stretching from the North Pole through Paris to the equator; It was also once defined as the distance between two marked lines on an international prototype, a bar of platinum-iridium alloy; still, it has been defined as 1,650,763.73 wavelengths of the orange-red line in the spectrum of the krypton-86 atom in the vacuum. The latest definition was decided by the General Conference on Weights and Measures in 1983 as the distance light travels in the vacuum in 1/299,792,458 second [17th CGPM, Resolution 1].
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