quantity for which all the exponents of the factors corresponding to the base quantities in its quantity dimension are zero

NOTE 1 The term “dimensionless quantity” is commonly used and is kept here for historical reasons. It stems from the fact that all exponents are zero in the symbolic representation of the dimension for such quantities. The term “quantity of dimension one” reflects the convention in which the symbolic representation of the dimension for such quantities is the symbol 1 (see ISO 31-0:1992, 2.2.6).

NOTE 2 The measurement units and values of quantities of dimension one are numbers, but such quantities convey more information than a number.

NOTE 3 Some quantities of dimension one are defined as the ratios of two quantities of the same kind.

EXAMPLES Plane angle, solid angle, refractive index, relative permeability, mass fraction, friction factor, Mach number.

NOTE 4 Numbers of entities are quantities of dimension one.

EXAMPLES Number of turns in a coil, number of molecules in a given sample, degeneracy of the energy levels of a quantum system.

- 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