1. Arbitrary activity of component B in system 1 (Ratio scale)
2. Arbitrary activity of component B in system 1 compared with arbitrary activity of component B in reference system (Ordinal scale)

Note 1:The concept has two definitions.

Note 2: “Activity” is an kind-of-quantiy related to rate. Cannot be related to catalytic-activity. For kind-of-quantity related to catalytic-activity, see Arbitrary catalytic-activity or Arbitrary catalytic-activity concentration.

Note 3: The reference system is defined by the laboratory.

• Value set is ranked accoding to magnitude
• The value set and the limit of the value set are defined by the laboratory
• The value set can be either numerical values or words.

Example 1

Value set={none < some < high < very high}

Example 2

Value set={low < normal< high }

Example 3

Value set={0 < 1 < 2}

Example 4

Value set={negative < positive}

Example 5

Value set={+ < ++ < +++}

• Algebraic operations are not allowed (Ref. 2, 1.26)
• Possible comparison of values (a<b, a=b or a>b)

• Value sets are positive numerical values
• Numerical values from 0-∞

• Algebraic operations are allowed
• Possible comparison of values (a=nb; a≠nb)

“Procedure” is stated in the specification to the kind-of-property in the NPU definition.

“Procedure” indicates that the measurement procedure must be stated somewhere else than the NPU code and there may be difficulties in comparing values for the same NPU code.

If the ratio scale is attributed to the NPU definition, the unit can be a non-SI unit.

If the unit is an International Unit (IU), an international certified reference material (e.g. WHO reference material) is specified in the specification to the kind-of-property.

If there exist no international certified reference material, the laboratory can specify the unit at the placeholder, procedure defined unit.

If ordinal scale is attributed, no unit is stated.

1. Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p.
2. Mesures BIdPe. International Vocabulary of Metrology – Basic and General Concepts and Associated Terms VIM 3rd edition JCGM 200:2012 (JCGM 200:2008 with minor corrections). https://www.bipm.org: Bureau International des Poids et Mesures; 2008.