Science pills: A brief history of meter

Since 1983, the meter has been the length of the empty path of light for 1 / 299,792,458 seconds, but this isn't the only definition it has had throughout its history. Perhaps the best known definitions are those of the early 19th century as the tenth millionth part of the quadrant of the Earth's meridian and the one that was in force between 1889 and 1960: a distance between the two pieces of the iridescent platinum bar deposited in the BIPM, in Sèvres, near Paris.

Between 1960 and 1983 the official definition of the meter was one million 650,763.73 wavelengths in the vacuum of the radiation corresponding to the transition between levels 2p10 and 5d5 of a krypton atom 86. The reason for this evolution throughout history is due to the improved accuracy and definition of the meter for better use in the scientific and industrial branches.