| qualifies the ratio of a quantity to a reference quantity other than a unit of measurement
NOTE 1 – Any relative quantity is of dimension one.
NOTE 2 – Examples: relative permittivity, relative permeability, relative density, relative resistances and relative reactances in the theory of electric machines.
NOTE 3 – The symbol of a relative quantity is generally deduced from the symbol of the original quantity by adding the subscript r. Examples: εr, µr.
NOTE 4 – The qualifier "per unit" (p.u.) is sometimes used but is not recommended.