Note 1 to entry: According to the type of reference, the value of a quantity is either:

1. a product of a number and a unit of measurement (the unit one is generally omitted for quantities of dimension one, as in examples f and g):

   a) Length of a given rod: 5,34 m or 534 cm

   b) Mass of a given body: 0,152 kg or 152 g

   c) Curvature of a given arc: 112 m^–1, expressed in words by "one hundred and twelve per metre"

   d) Celsius temperature of a given sample: –5 °C

   e) Electric impedance of a given circuit element at a given frequency, where j is the imaginary unit: (7,5 + 3,2 j) Ω

   f) Refractive index of a given sample of glass: 1,32

   g) Mass fraction of cadmium in a given sample of copper: 3 µg/kg or 3 × 10^–1

   h) Molality of Pb²⁺ in a given sample of water: 1,76 mmol/kg

2. a number and a reference to a measurement procedure:

   Rockwell C hardness of a given sample: 43,5 HCR

3. a number and a reference material:

   Arbitrary amount-of-substance concentration of lutropin in a given sample of human blood plasma (WHO International Standard 80/552 used as a calibrator): 5,0 IU/l, where "IU" stands for "WHO International Unit"

In the first case, the value of a quantity Q is generally denoted {Q}[Q] where {Q} is the numerical value and [Q] is the unit of measurement.

Note 2 to entry: The number can be complex (see example e in Note 1 to entry).

Note 3 to entry: The value of a quantity can be presented in more than one way (see examples a, b, and g in Note 1 to entry).

Note 4 to entry: In the case of vector or tensor quantities, each component has a value, and the same for the magnitude of a vector quantity. Example:

force acting on a given particle, e.g. in Cartesian components
(F_x; F_y; F_z) = (–31,5; 43,2; 17,0) N