From Wikipedia: "Since 1983, [the metre] is defined as the distance travelled by light in vacuum in 1⁄299,792,458 of a second." This is the currently used definition.
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A meter is currently defined as the length of the path travelled by light in vacuum during a time interval of 1 / 299,792,458 of a second.
A meter is defined as the distance travelled by light in free space in 1/299,792,458th of a second.
Until 1983 the metre was defined at one ten millionth of the distance from the equator to the north pole. That definition has changed to reflect greater understanding and knowledge. Originally, the meter was based on the distance between the equator and the north pole along the meridian that went through Paris. That distance was set at 10,000 kilometers and the metre was ten millionth of the distance.
The meter was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator to the North Pole through Paris.In 1983, the meter was redefined as the distance traveled by light in free space in 1⁄299,792,458 of a second.
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