# 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), Division 4: UNITS AND NAMES OF UNITS PERMITTED IN SPECIALIZED FIELDS ONLY

Extent: E+W+S+N.I.

Quantity
Unit
Name
Symbol
Value
Vergency of optical systems
dioptre*
1 dioptre = 1 m -1
Mass of precious stones
metric carat
1 metric carat = 2 × 10 -4 kg
Area of farmland and building land
are
a
1 a = 10 2 m 2
Mass per unit length of textile yarns and threads
tex*
tex*
1 tex = 10 -6 kg · m -1
Blood pressure and pressure of other body fluids
Millimetre of mercury
mm Hg(*)
1 mm Hg = 133,322 Pa
Effective cross-sectional area
Barn
b
1 b = 10 -28 m 2

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Source: https://www.legislation.gov.uk/eudr/1980/181/annex/chapter/I/division/4 (the official version)
Page: https://openlegislation.uk/eu-directive-1980-181/annex/chapter-I/division-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.