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(measurable) quantity :

Attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively.


Base quantity :

One of the quantities that, in a system of quantities, are conventionally accepted as functionally independent of one another.

The quantities length, mass and time are generally taken to be base quantities in the field of mechanics.


Derived quantity :

Quantity defined, in a system of quantities, as a function of base quantities of that system.

In a system having base quantities length, mass and time, velocity is a derived quantity defined as: length divided by time.

Unit (of measurement) :

Particular quantity, defined and adopted by convention, with which other quantities of the same kind are compared in order to express their magnitudes relative to that quantity.


Symbol of a unit (of measurement) :

Conventional sign designating a unit of measurement.

a) m is the symbol of metre ;
b) A is the symbol of ampere.

International System of Units, SI :

The coherent system of units adopted and recommended by the Conférence Générale des Poids et Mesures (CGPM).


The SI is based at the present on the following seven base units :

SI base unit
Quantity Name Symbol
length metre m
mass kilogram kg
time second s
electric current ampere A
thermodynamic temperature kelvin K
amount of substance mole mol
luminous intensity candela cd

Base unit (of measurement) :

Unit of measurement of a base quantity in a given system of quantities.


In any given coherent systems of units there is only one base unit for each base quantity.

Derived unit (of measurement) :

Unit of measurement of a derived quantity in a given system of quantities.


Some derived units have special names and symbols ; for example in the SI :

SI derived unit
Quantity Name Symbol
force newton N
energy joule J
pressure pascal Pa

Multiple of a unit (of measurement) :

Larger unit of measurement that is formed from a given unit according to scaling conventions.

a) One of the decimal multiples of the metre is the kilometre ;
b) One of the non-decimal multiples of the second is the hour.

Submultiple of a unit (of measurement) v:

Smaller unit of measurement that is formed from a given unit according to scaling conventions.

One of the decimal submultiples of the metre is the millimetre.

Value (of a quantity) :

Magnitude of a particular quantity generally expressed as a unit of measurement multiplied by a number.

a) Length of a rod: 5,34 m or 534 cm ;
b) Mass of a body: 0,152 kg or 152 g ;
c) Amount of substance of a sample of water (H2O): 0,012 mol or 12 mmol.



Measurement :

Set of operations having the object of determining a value of a quantity.


Metrology :

Science of measurement.


Measurand :

Particular quantity subject to measurement.


Vapour pressure of a given sample of water at 20 °C.


Accuracy of measurement :

Closeness of the agreement between the result of a measurement and a true value of the measurand.


Repeatability (of results of measurements):

Closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement.


Reproducibility (-of results of measurements) :

Closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement.


Uncertainty of measurement :

Parameter, associated with the result of a measurement, that characterizes the dispersion of values that could reasonably be attributed to the measurand.


Error (of measurement) :

Result of a measurement minus a true value of the measurand.


Deviation :

Value minus its reference value.


Many different terms are employed to describe the artefacts which are used in measurement. This Vocabulary defines only a selection of preferred terms; the following list is more complete and is arranged in an approximate order of increasing complexity. These terms are not mutually exclusive.

Material measure :

Device intended to reproduce or supply, in a permanent manner during its use, one or more known values of a given quantity.

a) a weight ;
b) a measure of volume (of one or several values, with or without a scale) ;
c) a standard electrical generator ;
d) a gauge block ;
e) a standard signal generator ;
f ) a reference material.



Some of the terms used in this chapter to describe the characteristics of a measuring instrument are equally applicable to a measuring device, a measuring transducer or a measuring system and by analogy may also be applied to a material measure or a reference material. Consequently, the term "measuring instrument" must be understood here as a generic term covering all of these possible meanings.
The input signal to a measuring system may be called the stimulus ; the output signal may be called the response.
In this chapter, the term “measurand” means the quantity that is applied to a measuring instrument.

Measuring range, working range :

Set of values of measurands for which the error of a measuring instrument is intended to lie within specified limits.



In science and technology, the English word "standard" is used with two different meanings: as a widely adopted written technical standard, specification, technical recommendation or similar document (in French "norme") and also as a measurement standard (in French "etalon"). This Vocabulary is concerned solely with the second meaning and the qualifier "measurement" is generally omitted for brevity.

(Measurement) standard :

Material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit or one or more values of a quantity to serve as a reference.

a) 1 kg mass standard ;
b) 100 Ω standard resistor ;
c) standard amperemeter ;
d) caesium frequency standard ;
e) standard hydrogen electrode ;
f) reference solution of cortisol in human serum having a certified concentration.


National (measurement) standard :

Standard recognized by a national decision to serve, in a country, as the basis for assigning values to other standards of the quantity concerned.

Primary standard :

Standard that is designated or widely acknowledged as having the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity.


Secondary standard :

Standard whose value is assigned by comparison with a primary standard of the same quantity.

Reference standard :

Standard, generally having the highest metrological quality available at a given location or in a given organization, from which measurements made there are derived.

Working standard :

Standard that is used routinely to calibrate or check material measures, measuring instruments or reference materials.


Transfer standard :

Standard used as an intermediary to compare standards.


Traceability :

Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.


Calibration :

Set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards.


Reference material (RM) :

Material or substance one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials.


Reference material (CRM) :

Reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which established traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence.