The meaning of measurement in metrology

The latest version of the International Vocabulary of Metrology gives a meaning of measurement restricted to quantities that can be represented by numerical values and placed in an ordinal sequence. This restrictive definition fits poorly with both the colloquial and the wider scientific understanding of measurement. This paper suggests an extension to the metrological definition of measurement, based on the measurement classification scheme of Stevens, to incorporate non-numerical and nominal measurements. The more inclusive definition and the classification scheme offers insights into the utility, metrological traceability, and limitations of measurements and uncertainty treatments, and enables clarification of other measurement-related definitions.