Evolution of the international system of units ( SI )

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Evolution of the international system of units ( SI )

Basic Magnitudes

Length

Meter

Mass

Kilometer

Time

Seconds

Temperature

Kelvin

Current intensity

Ampere

Luminous intensity

Candela

Amount of substance

Mole

It allows :

The equivalence of measurements

Performed with similar instruments used and calibrated at different locations

It was established in:

During the:

General Conference on Weights and Measures ( CGPM )

Brief history in the evolution of SI

They entrust the CIPM with a study to regulate the units of measurement. Set the ampere

It adopts 6 base unit system. choose the triple point of water

It adopts the name of the international system of units and the acronym si. redefines the meter and second. set rules for prefixes

11a. CGPM, 1960

Decide on the liter and the cubic decimeter. the prefix femto and atto are introduced.

12a. CGPM 1964

Define the second in terms of the cesium atom 133. redefine the candela. add derived units. defines the unit of thermodynamic temperature

13a, CGPM 1967

Define and enter the mole as the seventh base unit. enter pascal and siemens

14a, CGPM 1971

Sets Coordinated Universal Time as the time scale (UTC) Enters the becquerel and gray . the prefixes exa and peta are added

15a, CGPM 1975

Redefines the candle. enter the sievert. the symbols l and L are established for the liter

16a, CGPM 1979

Redefine the meter based on the speed of light

17a, CGPM 1983

Enter the prefixes Z Y z y

19a, CGPM 1991

Eliminates the class of supplementary units within the SI context

20a, CGPM 1995

Sets the katal as derived SI units

21a, CGPM 1999

10a. CGPM, 1954

9a. CGPM, 1948