EXAMPLE The volume of water delivered by a 50 ml pipette at 20 °C is measured by weighing the water delivered by the pipette into a beaker, taking the mass of beaker plus water minus the mass of the initially empty beaker, and correcting the mass difference for the actual water temperature using the volumic mass (mass density).

NOTE 1 The Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM) uses the term “primary method of measurement” for this concept.

NOTE 2 Definitions of two subordinate concepts, which could be termed “direct primary reference measurement procedure” and “ratio primary reference measurement procedure”, are given by the CCQM (5th Meeting, 1999) ^[43].

ANNOTATION (for Note 1) (informative) [9 June 2016] The terms "primary method", "primary method of measurement", and "primary measurement method" are more generally used for a method adopted to obtain a measurement result without relation to a measurement standard for a quantity of the same kind.