reference measurement procedure used to obtain a measurement result without relation to a measurement
standard for a quantity of the same kind

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).