On March 30, 1791, the French Academy of Sciences defined the length of a meter. Before this date, there were two definitions to this measure of length: The first was based on the length of a pendulum and the second was based on a fraction of the length of a half-meridian, or line of longitude. The French Academy chose the meridian definition. This defined one meter as one ten-millionth of the distance from the Equator to the North Pole.

The meter is the basic unit of distance in the International System of Units (SI), the world’s standardized system of measurement. Since the 1960s, all countries have adopted or legally recognized the SI. As a universal standard of measure, the meter helped ease the exchange of commerce and scientific data.

However, the definition of a meter has changed since 1791. In 1983, the meter got its current definition. The meter is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second.