Council Directive of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC (80/181/EEC)

[X1 1.1. SI base units U.K.

Quantity	Unit
	Name	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Thermodynamic temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

Definitions of SI base units: U.K.

[F1 Unit of length U.K.

A metre is the length of the path travelled in a vacuum by light during 1/ 299 792 458 seconds.

(Seventeenth CGPM (1983), Resolution 1).]

Textual Amendments

F1 Substituted by Council Directive of 18 December 1984 amending Directive 80/181/EEC on the approximation of the laws of the Member States relating to units of measurement (85/1/EEC).

Unit of mass U.K.

The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

(Third CGPM (1901), page 70 of the conference report).

Unit of time U.K.

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

(Thirteenth CGPM (1967), resolution 1).

Unit of electric current U.K.

The ampere is that constant current, which if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between those conductors a force equal to 2 × 10 ^-7 newton per metre of length.

(CIPM (1946), resolution 2, approved by the ninth CGPM (1948)).

[F2 Unit of thermodynamic temperature U.K.

The kelvin, unit of thermodynamic temperature, is the fraction 1/273,16 of the thermodynamic temperature of the triple point of water.

This definition refers to water having the isotopic composition defined by the following amount-of-substance ratios: 0,00015576 mole of  ² H per mole of  ¹ H, 0,0003799 mole of ¹⁷ O per mole of ¹⁶ O and 0,0020052 mole of ¹⁸ O per mole of  ¹⁶ O.

(Thirteenth CGPM (1967), resolution 4 and Twenty-third CGPM (2007), resolution 10)]

Textual Amendments

F2 Substituted by Directive 2009/3/EC of the European Parliament and of the Council of 11 March 2009 amending Council Directive 80/181/EEC on the approximation of the laws of the Member States relating to units of measurement (Text with EEA relevance).

Unit of amount of substance U.K.

(1)

The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0·012 kilogram of carbon 12.

(2)

When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

(Fourteenth CGPM (1971), resolution 3).

Unit of luminous intensity U.K.

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency of 540 × 10 ¹² hertz and that has a radiant intensity in that direction of (1/683) watt per steradian.

(Sixteenth CGPM (1979), resolution 3).

1.1.1. [F2 Special name and symbol of the SI derived unit of temperature for expressing Celsius temperature] U.K.

Quantity	Unit
	Name	Symbol
Celsius temperature	degree Celsius	°C

[F3 Celsius temperature [X2 t] is defined as the difference [X2 t = T - T _0] between the two thermodynamic temperatures [X2 T] and [X2 T ₀ where T _0]  = 273,15 K. An interval or difference of temperature may be expressed either in kelvins or in degrees Celsius. The unit ‘ degree Celsius ’ is equal to the unit ‘ kelvin ’ .] ]

Editorial Information

X2 Substituted by Corrigendum to Directive 1999/103/EC of the European Parliament and of the Council of 24 January 2000 amending Council Directive 80/181/EEC on the approximation of the laws of the Member States relating to units of measurement (Official Journal of the European Communities L 34 of 9 February 2000).

Textual Amendments

F3 Substituted by Directive 1999/103/EC of the European Parliament and of the Council of 24 January 2000 amending Council Directive 80/181/EEC on the approximation of the laws of the Member States relating to units of measurement.

Editorial Information

X1 Substituted by Corrigendum to Council Directive 80/181/EEC of 20 December 1979 on the aproximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC (Official Journal of the European Communities No L 39 of 15 February 1980).