The most important milestones of recent metrology history.
|1670||Proposition for a new length unit based on the terrestrial meridian|
|1799||Creation of the decimal metric system
Two platinum standards, representing the metre and the kilogram manufactured
|1832||Austrian mathematician Gauss strongly promotes the application of the metric system, together with the second defined in astronomy, as a coherent system of units for the physical sciences; first measurements of the Earth's magnetic field take place|
|1860||Maxwell and Thomson formulate the requirement for a coherent system of units with base units and derived units|
|1880||Approval by IEC of a mutually coherent set of practical units. Among them were the Ohm for electrical resistance, the Volt for electromotive force, and the Ampere for electric current|
|1875||Signing of the Metre Convention, which created the BIPM, established the CGPM and the CIPM, and adopted the MKS system|
|1889||The first conference of CPGM takes place|
|1901||The so-called rationalised proposal of Giorgi, for a single coherent four-dimensional system, by adding to the three base units a fourth unit, of an electrical nature such as the Ampere or the Ohm, and rewriting the equations occurring in electromagnetism|
|1939||Adoption of a four-dimensional system based on the metre, kilogram, second, and Ampere, and the MKSA system, a proposal approved by the CIPM in 1946|
|1954||Introduction of the Ampere, the Kelvin, and the Candela as base units, respectively, for electric current, thermodynamic temperature, and luminous intensity|
|1960||The name International System of Units, with the abbreviation SI, is given to the system|
|1971||Introduction of the last SI base unit: the mole, as the base unit for amount of substance, bringing the total number of base units to seven|
|1999||Signature of the CIPM-MRA (Mutual Recognition Agreement), for international recognition of national measurement standards|
|2018||New definition adopted concerning four base units on 7 (see hereunder Sect. 6.3)|
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