 A topic that has attracted considerable philosophical attention in recent years is the selection and improvement of measurement standards. Generally speaking, to standardize a quantity concept is to prescribe a determinate way in which that concept is to be applied to concrete  particulars.[21]  To standardize a measuring instrument is to assess how well the outcomes of measuring with that instrument fit the prescribed mode of application of the relevant concept.  [22]  The term “measurement standard” accordingly has at least two meanings: on the one hand, it is commonly used to refer to abstract rules and definitions that regulate the use of quantity concepts, such as the definition of the meter. On the other hand, the term “measurement standard” is also commonly used to refer to the concrete artifacts and procedures that are deemed exemplary of the application of a quantity concept, such as the metallic bar that served as the standard meter until 1960. This duality in meaning reflects the dual nature of standardization, which involves both abstract and concrete aspects.