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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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