NOTE 1 Examination of a nominal property provides a nominal property value and associated uncertainty. This uncertainty is not a measurement uncertainty.
NOTE 2 Reference materials with or without assigned quantity values can be used for measurement precision control whereas only reference materials with assigned quantity values can be used for calibration or measurement trueness control.
NOTE 3 'Reference material' comprises materials embodying quantities as well as nominal properties.
EXAMPLE 1 Examples of reference materials embodying quantities:
a) water of stated purity, the dynamic viscosity of which is used to calibrate viscometers;
b) human serum without an assigned quantity value for the amount-of-substance concentration of the inherent cholesterol, used only as a measurement precision control material;
c) fish tissue containing a stated mass fraction of a dioxin, used as a calibrator.
EXAMPLE 2 Examples of reference materials embodying nominal properties:
a) colour chart indicating one or more specified colours;
b) DNA compound containing a specified nucleotide sequence;
c) urine containing 19-androstenedione.
NOTE 4 A reference material is sometimes incorporated into a specially fabricated device.
EXAMPLE 1 Substance of known triple-point in a triple-point cell.
EXAMPLE 2 Glass of known optical density in a transmission filter holder.
EXAMPLE 3 Spheres of uniform size mounted on a microscope slide.
NOTE 5 Some reference materials have assigned quantity values that are metrologically traceable to a measurement unit outside a system of units. Such materials include vaccines to which International Units (IU) have been assigned by the World Health Organization.
NOTE 6 In a given measurement, a given reference material can only be used for either calibration or quality assurance.
NOTE 7 The specifications of a reference material should include its material traceability, indicating its origin and processing (Accred. Qual. Assur.:2006) .
NOTE 8 ISO/REMCO has an analogous definition  but uses the term “measurement process” to mean 'examination' (ISO 15189:2007, 3.4), which covers both measurement of a quantity and examination of a nominal property.