quantity value consistent with the definition of a quantity

NOTE 1 In the Error Approach to describing measurement, a true quantity value is considered unique and, in practice, unknowable. The Uncertainty Approach is to recognize that, owing to the inherently incomplete amount of detail in the definition of a quantity, there is not a single true quantity value but rather a set of true quantity values consistent with the definition. However, this set of values is, in principle and in practice, unknowable. Other approaches dispense altogether with the concept of true quantity value and rely on the concept of metrological compatibility of measurement results for assessing their validity.

NOTE 2 In the special case of a fundamental constant, the quantity is considered to have a single true quantity value.

NOTE 3 When the definitional uncertainty associated with the measurand is considered to be negligible compared to the other components of the measurement uncertainty, the measurand may be considered to have an “essentially unique” true quantity value. This is the approach taken by the GUM and associated documents, where the word “true” is considered to be redundant.

ANNOTATION (informative) [5 June 2014] Here "quantity value" can be replaced with "value" without ambiguity: "value consistent with the definition of a quantity".

ANNOTATION (for Note 1) (informative) [5 June 2014]: Two reasons that the set of true values is unknowable are: 1) the measurement model used in a measurement may be incorrect, and 2) a mistake may be made in performing the measurement.

- 1.1 quantity
- 1.2 kind of quantity
- 1.3 system of quantities
- 1.4 base quantity
- 1.5 derived quantity
- 1.6 International System of Quantities
- 1.7 quantity dimension
- 1.8 quantity of dimension one
- 1.9 measurement unit
- 1.10 base unit
- 1.11 derived unit
- 1.12 coherent derived unit
- 1.13 system of units
- 1.14 coherent system of units
- 1.15 off-system measurement unit
- 1.16 International System of Units
- 1.17 multiple of a unit
- 1.18 submultiple of a unit
- 1.19 quantity value
- 1.20 numerical quantity value
- 1.21 quantity calculus
- 1.22 quantity equation
- 1.23 unit equation
- 1.24 conversion factor between units
- 1.25 numerical value equation
- 1.26 ordinal quantity
- 1.27 quantity-value scale
- 1.28 ordinal quantity-value scale
- 1.29 conventional reference scale
- 1.30 nominal property

- 2.1 measurement
- 2.2 metrology
- 2.3 measurand
- 2.4 measurement principle
- 2.5 measurement method
- 2.6 measurement procedure
- 2.7 reference measurement procedure
- 2.8 primary reference measurement procedure
- 2.9 measurement result
- 2.10 measured quantity value
- 2.11 true quantity value
- 2.12 conventional quantity value
- 2.13 measurement accuracy
- 2.14 measurement trueness
- 2.15 measurement precision
- 2.16 measurement error
- 2.17 systematic measurement error
- 2.18 measurement bias
- 2.19 random measurement error
- 2.20 repeatability condition of measurement
- 2.21 measurement repeatability
- 2.22 intermediate precision condition of measurement
- 2.23 intermediate measurement precision
- 2.24 reproducibility condition of measurement
- 2.25 measurement reproducibility
- 2.26 measurement uncertainty
- 2.27 definitional uncertainty
- 2.28 Type A evaluation of measurement uncertainty
- 2.29 Type B evaluation of measurement uncertainty
- 2.30 standard measurement uncertainty
- 2.31 combined standard measurement uncertainty
- 2.32 relative standard measurement uncertainty
- 2.33 uncertainty budget
- 2.34 target measurement uncertainty
- 2.35 expanded measurement uncertainty
- 2.36 coverage interval
- 2.37 coverage probability
- 2.38 coverage factor
- 2.39 calibration
- 2.40 calibration hierarchy
- 2.41 metrological traceability
- 2.42 metrological traceability chain
- 2.43 metrological traceability to a measurement unit
- 2.44 verification
- 2.45 validation
- 2.46 metrological comparability of measurement results
- 2.47 metrological compatibility of measurement results
- 2.48 measurement model
- 2.49 measurement function
- 2.50 input quantity in a measurement model
- 2.51 output quantity in a measurement model
- 2.52 influence quantity
- 2.53 correction

- 3.1 measuring instrument
- 3.2 measuring system
- 3.3 indicating measuring instrument
- 3.4 displaying measuring instrument
- 3.5 scale of a displaying measuring instrument
- 3.6 material measure
- 3.7 measuring transducer
- 3.8 sensor
- 3.9 detector
- 3.10 measuring chain
- 3.11 adjustment of a measuring system
- 3.12 zero adjustment of a measuring system

- 4.1 indication
- 4.2 blank indication
- 4.3 indication interval
- 4.4 nominal indication interval
- 4.5 range of a nominal indication interval
- 4.6 nominal quantity value
- 4.7 measuring interval
- 4.8 steady-state operating condition
- 4.9 rated operating condition
- 4.10 limiting operating condition
- 4.11 reference operating condition
- 4.12 sensitivity of a measuring system
- 4.13 selectivity of a measuring system
- 4.14 resolution
- 4.15 resolution of a displaying device
- 4.16 discrimination threshold
- 4.17 dead band
- 4.18 detection limit
- 4.19 stability of a measuring instrument
- 4.20 instrumental bias
- 4.21 instrumental drift
- 4.22 variation due to an influence quantity
- 4.23 step response time
- 4.24 instrumental measurement uncertainty
- 4.25 accuracy class
- 4.26 maximum permissible measurement error
- 4.27 datum measurement error
- 4.28 zero error
- 4.29 null measurement uncertainty
- 4.30 calibration diagram
- 4.31 calibration curve

- 5.1 measurement standard
- 5.2 international measurement standard
- 5.3 national measurement standard
- 5.4 primary measurement standard
- 5.5 secondary measurement standard
- 5.6 reference measurement standard
- 5.7 working measurement standard
- 5.8 travelling measurement standard
- 5.9 transfer measurement device
- 5.10 intrinsic measurement standard
- 5.11 conservation of a measurement standard
- 5.12 calibrator
- 5.13 reference material
- 5.14 certified reference material
- 5.15 commutability of a reference material
- 5.16 reference data
- 5.17 standard reference data
- 5.18 reference quantity value