Arbitrary length (arb.length) - Dynamic NPU Manual

Arbitrary length (arb.length)



Definition in words

Arbitrary length of component B in system 1

Definition by equation

Note: kprocedure is a constant defined by the measurement procedure (there is an approximately proportionality to a kind-of-quantity from the International System of Quantities).

Result type

Rational scale

  • Value sets are positive numerical values
  • Numerical values from 0-∞
  • Algebraic operations are allowed
  • Possible comparison of values (a=nb; a≠nb)


International unit (IU) or procedure defined unit (p.d.u.) (non-SI units)

Special rule(s) in the NPU syntax

“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 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.


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. doi:10.1039/9781782622451.

Laboratory field


Clinical Chemistry

Generic abbreviated form NPU17589 B—Sedimentation reaction; arb.length(proc.) = ? (p.d.u.) 
Full form with a result NPU17589 Blood—Sedimentation reaction; arbitrary length(procedure) = 156 arbitrary unit
Abbreviated form with a result NPU17589 B—Sedimentation reaction; arb.length(proc.) = 156 arbitrary unit
Written expression The arbitrary length of Sedimentation reaction in Mr Smith’s blood is [156] arbitrary unit. The measurement is performed according to a procedure defined by the given laboratory.

“Arbitrary unit” was chosen by a local laboratory as a proprietary measurement unit and not an accepted international unit.
  • Kind-of-property

    • Nominal kind-of-property

    • Kind-of-quantity

      • Ordinal kind-of-quantity

      • Unitary kind-of-quantity

        • Rational unitary kind-of-quantity

          • Arbitrary length


  • Dybkaer R. Concept system on ‘quantity’: formation and terminology. Accredit Qual Assur. 2013;18(3):253-60.
  • Dybkaer R. ISO terminological analysis of the VIM3 concepts ‘quantity’ and ‘kind-of-quantity’. Metrologia. 2010;47(3):127-34.
Date Term Note
1996-01-01 Arbitrary length Term established.