Meter, also spelled metre, is the base unit of length in the metric system. Its symbol is m. A meter is equal to 39.370 inches. Scientists define the meter as the distance traveled by light in a vacuum during 1/299,792,458 of a second. From 1960 to 1983, the length of the meter had been defined as 1,650,763.73 wavelengths of the orange-red line of the spectrum of light radiated by the isotope krypton 86, measured in a vacuum. This measurement standard had replaced the platinum-iridium meter bar. See also Centimeter ; Metric system .
