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Table 1
The most important milestones of recent metrology history.
| Date | Event |
|---|---|
| 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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