The linear meter is **the fundamental unit of length measurement** of the International System of Measurements, abbreviated **YES**. The linear meter symbol is **m** and is defined as the **distance light travels in a vacuum in a fraction of 1/299,792,458 seconds** (The speed of light is 299,792,458 meters per second).

The linear meter is often referred to simply as a meter, using the linear meter if it is necessary to clearly differentiate it from surface measurements (square meter) or volume measurements (cubic meter).

## definition of meter

The word meter derives from the Greek *μέτρον* (metron), which literally means "measure." The first definition as a unit of length was given in 1971 by the French Academy of Sciences. Since then, the meter has been redefined several times, always seeking greater precision, until reaching the current definition based on the speed of light in a vacuum:

**1791 definition (French Academy of Sciences)**: ten-millionth of the distance that separates the North Pole from the line of the terrestrial equator. This definition had an absolute uncertainty of 0.5–0.1 mm (relative uncertainty of 10^{-4}).**Definition of 1792 and 1795**: In 1792 the French Academy of Sciences accepted a provisional prototype of a brass bar as a standard measure of 1 m built according to Bessel's measurements of one ten-millionth of the distance between the North Pole and the equator (443.44 lines). In 1795 a platinum bar was accepted as the final standard based on Delambre and Mechain's measurements of the north pole-equator distance (443,296 lines).**Definition of 1799**: First prototype platinum bar. The uncertainty is reduced to 0.05–0.01 mm (relative uncertainty of 10^{-5}).**1889 definition (1st General Conference on Weights and Measures)**: the meter is measured in a bar of an alloy of platinum with 10% iridium at the melting temperature of ice. The absolute uncertainty falls to 0.2–0.1 µm and the relative uncertainty to 10^{-7}.**1960 definition (11th General Conference on Weights and Measures)**: the International System of Units is established and the meter is defined as 1 650 763.73 wavelengths of the radiation in the vacuum emitted by the transition between the 2p quantum levels^{10}at 5d^{5}of the krypton atom 86 (orange radiation). The uncertainty becomes 0.01–0.005 µm (relative uncertainty of 10^{-8}).**1983 definition (17th General Conference on Weights and Measures)**: The meter is defined as the distance traveled by light in a vacuum in a period of 1/299,792,458 seconds. The absolute uncertainty goes down to 0.1 nm, the relative uncertainty down to 10^{-10}.

Maintaining the 1983 definition, in 2002 the International Committee for Weights and Measures (CIPM) considers that the definition of meter **it is only applicable as a measure of proper length in the context of general relativity**^{5}. This is due to the phenomenon known as Lorentz contraction, which describes how the length of an object shortens in the direction of motion as its speed approaches the speed of light. This phenomenon means that the length of a body in motion is always less than that at rest, with the length at rest being referred to as **proper length**.

All these definitions and nuances have their importance in the scientific field but have not had an effect on the day-to-day life of the general population. The meter is currently one of the most recognizable units of measurement in the world, even in countries where the adoption of the International System of Units has not been effective or is being very slow, as is the case in the United States.

## Multiples and submultiples of the meter in the International System of Units

submultiples | multiples | |||||
---|---|---|---|---|---|---|

Worth | Symbol | Name | Worth | Symbol | Name | |

10^{−1} m | dm | decimeter | 10^{1} m | dam | decameter | |

10^{−2} m | cm | centimeter | 10^{two} m | hmm | hectometer | |

10^{−3} m | hmm | millimeter | 10^{3} m | km | kilometer | |

10^{−6} m | µm | micrometer | 10^{6} m | mmm | megameter | |

10^{−9} m | nm | nanometer | 10^{9} m | GM | gigameter | |

10^{−12} m | p.m | picometer | 10^{12} m | tm | terameter | |

10^{−15} m | fm | femtometer | 10^{fifteen} m | P.m | petameter | |

10^{−18} m | A.M | attometer | 10^{18} m | em | hexameter | |

10^{−21} m | zm | zeptometer | 10^{twenty-one} m | Zm | zettameter | |

10^{−24} m | and m | yoctometer | 10^{24} m | ym | yottameter |