On March 30, 1791, the French Academy of Sciences defined the length of a meter. Before this date, there were two definitions to a meter: one based on the length of a pendulum and the other based on a fraction of the length of a half-meridian, or line of longitude. The 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, most countries have adopted the SI. This has helped ease the exchange of commerce and scientific data.

The definition of a meter has changed since 1791. Today, a meter is “the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.”

commerce
Noun

trade, or the exchange of goods and services.

data
Plural Noun

(singular: datum) information collected during a scientific study.

Noun

imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.

Noun

distance east or west of the prime meridian, measured in degrees.

measurement
Noun

process of determining length, width, mass (weight), volume, distance or some other quality or size.

meridian
Noun

line of longitude, dividing the Earth by north-south.

Noun

fixed point that, along with the South Pole, forms the axis on which the Earth spins.

pendulum
Noun

object suspended from a point, able to swing back and forth.

vacuum
Noun

area of empty space.

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