4.
Units and names of units permitted in specialised fields only 

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 x 10-4 kg

Area of farmland and building land

are

a

1 a = 102 m2

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

Pressure in the fields of plasma physics and semiconductors

millimetre of mercury

mm Hg

1 mm Hg = 133.322387 Pa

Torr

Torr

1 Torr = 133.322368 Pa

Effective cross-sectional area

Barn

b

1b = 10-28 m2

The prefixes and their symbols listed in F‑II, Annex 2, 1.3, may be used in conjunction with the above units and symbols, with the exception of the millimetre of mercury and its symbol. The multiple of 102 a is, however, called a "hectare".

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