Note: |
NOTE 1 The term “dimensionless quantity” is commonly used and is kept here for historical reasons. It stems from the fact that all exponents are zero in the symbolic representation of the dimension for such quantities. The term “quantity of dimension one” reflects the convention in which the symbolic representation of the dimension for such quantities is the symbol 1, see Clause 5 (of ISO 80000-1:2009). This dimension is not a number, but the neutral element for multiplication of dimensions.|, NOTE 2 The measurement units and values of quantities of dimension one are numbers, but such quantities convey more information than a number.|, NOTE 3 Some quantities of dimension one are defined as the ratios of two quantities of the same kind. The coherent derived unit is the number one, symbol 1., EXAMPLE Plane angle, solid angle, refractive index, relative permeability, mass fraction, friction factor, Mach number.|, NOTE 4 Numbers of entities are quantities of dimension one., EXAMPLE Number of turns in a coil, number of molecules in a given sample, degeneracy of the energy levels of a quantum system.|, NOTE 5 Adapted from ISO/IEC Guide 99:2007, definition 1.8, in which Notes 1 and 3 are different and in which “dimensionless quantity” is given as an admitted term. |