International Vocabulary of Basic and General Terms in Metrology (VIM)

FOREWORD
The evolution of the treatment of metrological uncertainty from a Classical Approach (CA) to an Uncertainty Approach (UA) necessitated reconsideration of the related definitions in the 2nd edition (1993) of the VIM . The CA took it for granted that a measurand can ultimately be described by a single true value, but that instruments and measurements do not yield this value due to additive “errors”, systematic and
random. These errors had to be treated differently in “error propagation” and it was assumed that they may always be distinguished. The notions of “random uncertainty” and “systematic uncertainty” were introduced without well-founded methods of combination and interpretation. Then, instead of random and systematic uncertainties, the unifying concept of “uncertainty” in measurement was introduced, an approach acknowledged by BIPM Recommendation INC-1 (1980), on the basis of which a detailed Guide to the Expression of Uncertainty in Measurement (GUM) (1993, corrected 1995) was developed.

In this operational approach to the evaluation of measurement uncertainties there is a shift of perception such that the notion of error no longer plays a role. As a consequence, there is finally only one uncertainty of measurement, ensuing from various components. It characterizes the extent to which the unknown value of the measurand is known after measurement, taking account of the given information from the measurement. The concepts and terms presented in Chapters 1-5 of this 3rd edition of the VIM reflect this UA. Note that it is beyond the scope of this Vocabulary to provide details for several of the concepts applying to the UA; for such details the interested reader is requested to consult the GUM.

There are certain concepts in the 2nd edition of the VIM that apply mostly to the CA, but also reflect some aspects of the UA. These concepts are avoided in the GUM, but are nonetheless considered to be of sufficient importance and common usage to be included in this Vocabulary. They are presented in Annex A, but in such a way as to be consistent with the CA. Some additional terms pertaining to the CA are also included in Annex A.

A number of concepts which figured in the 2nd edition of the VIM no longer appear in this 3rd edition. These are concepts which can probably no longer be considered as basic or general. Some new concepts reflecting the evolution of metrology have been introduced, in particular concepts related to measurement uncertainty or measurement traceability. Also, the various aspects of measurements in chemistry as well as in physics were considered when establishing this 3rd edition. As a result, a number of examples covering the fields of measurements in chemistry and in laboratory medicine have been added.

A few definitions in this draft are marked “preliminary definition” for they are still under study by JCGM-WG2. Concepts figuring in both the 2nd and 3rd editions have a double reference number; the 3rd edition reference number in bold font and, in parenthesis and in light font, the earlier reference from the 2nd edition.

The definitions proposed in this 3rd edition comply as far as possible with the rules to be applied in terminology work, as outlined in standards ISO 704, ISO 1087-1, and ISO 10241. In particular, the substitution principle should apply; it is possible in every definition to replace any term defined elsewhere in the VIM by its definition without introducing contradiction or circularity. Such terms are indicated in bold font in the definitions and notes.

To facilitate the understanding of the different relations between the various concepts given here, concept diagrams have been introduced in this 3rd edition. They are given in an Informative Annex.

Chapter 1: QUANTITIES AND UNITS
1.1 quantity
property of a phenomenon, body, or substance, to which a magnitude can be assigned

1.2 quantities of the same kind
quantities that can be placed in order of magnitude relative to one another

1.3 system of quantities
set of quantities together with a set of non-contradictory equations relating those quantities

1.4 International System of Quantities ISQ
system of quantities, together with the equations relating the quantities, on which the SI is based

1.5 base quantity
quantity, chosen by convention, used in a system of quantities to define other quantities

1.6 derived quantity
quantity, in a system of quantities, defined as a function of base quantities

1.7 quantity dimension, dimension of a quantity, dimension
dependence of a given quantity on the base quantities of a system of quantities, represented by the product of powers of factors corresponding to the base quantities

1.8 quantity of dimension one, dimensionless quantity
quantity for which all the exponents of the factors corresponding to the base quantities in the representation of its dimension are zero

1.9 unit, measurement unit, unit of measurement
scalar quantity, defined and adopted by convention, with which other quantities of the same kind are compared in order to express their magnitudes

1.10 quantity value, value of a quantity, value
magnitude of a quantity represented by a number and a reference

1.11 base unit, base measurement unit
unit that is conventionally and uniquely adopted for a base quantity in a given system of quantities

1.12 derived unit
unit for a derived quantity

1.13 coherent derived unit
derived unit that, for a given system of quantities and for a chosen set of base units, is a product of powers of base units with the proportionality factor one

1.14 system of units
conventionally selected set of base units and derived units, and also their multiples and submultiples, together with a set of rules for their use

1.15 coherent system of units
system of units, based on a given system of quantities, in which the unit for each derived quantity is a coherent derived unit

1.16 International System of Units, SI
coherent system of units based on the ISQ, their names and symbols, and a series of prefixes and their names and symbols, together with rules for their use, adopted by the General Conference on Weights and Measures (CGPM)

1.17 multiple of a unit
unit formed from a given unit by multiplying by an integer greater than one

1.18 submultiple of a unit
unit formed from a given unit by dividing by an integer greater than one

1.19 conventional quantity value, conventional value of a quantity, conventional value
value attributed by formal agreement to a quantity for a given purpose

1.20 numerical quantity value, numerical value of a quantity, numerical value
number in the representation of a quantity value

1.21 quantity equation
equation relating quantities

1.22 unit equation
equation relating units

1.23 numerical value equation, numerical quantity value equation
equation relating numerical quantity values

1.24 quantity calculus
formalism for algebraic manipulation of symbols representing quantities

1.25 conversion factor between units
ratio of two units for quantities of the same kind

1.26 ordinal quantity
quantity, defined by a conventional measurement procedure, for which a total ordering relation with other quantities of the same kind is defined, but for which no algebraic operations among those quantities are defined

Chapter 2: MEASUREMENT

2.1 measurement
process of experimentally obtaining information about the magnitude of a quantity

2.2 metrology
field of knowledge concerned with measurement

2.3 measurand
quantity intended to be measured

2.4 measurement principle, principle of measurement
phenomenon serving as the basis of a measurement

2.5 measurement method, method of measurement
generic description of a logical sequence of operations used in a measurement

2.6 measurement procedure
detailed description of a measurement according to one or more measurement principles and to a given measurement method

2.7 primary measurement procedure, primary procedure
measurement procedure used to realize the definition of a measurement unit and obtain the quantity value and measurement uncertainty of a primary measurement standard

2.8 measurement scale
ordered set of values of quantities of a given kind, continuous or discrete, used in arranging quantities of the same kind by magnitude

2.9 conventional reference measurement scale, conventional reference scale
measurement scale, defined by general agreement

2.10 measurement result, result of measurement
information about the magnitude of a quantity, obtained experimentally

2.11 measurement uncertainty, uncertainty of measurement, uncertainty
parameter that characterizes the dispersion of the quantity values that are being attributed to a measurand, based on the information used

2.12 definitional measurement uncertainty, definitional uncertainty
component of measurement uncertainty resulting from the inherently finite amount of detail in the definition of a measurand

2.13 Type A evaluation of measurement uncertainty, Type A evaluation
method of evaluation of a component of measurement uncertainty by a statistical analysis of quantity values obtained by measurements under repeatability conditions

2.14 Type B evaluation of measurement uncertainty, Type B evaluation
method of evaluation of a component of measurement uncertainty by means other than a statistical analysis of quantity values obtained by measurement

2.15 standard measurement uncertainty, standard uncertainty of measurement, standard uncertainty
measurement uncertainty expressed as a standard deviation

2.16 combined standard measurement uncertainty, combined standard uncertainty
standard measurement uncertainty of the measurement result when that result is obtained from the values of a number of other quantities, equal to the positive square root of a sum of terms, the terms being the variances and/or covariances of the values of these other quantities weighted according to how the measurement result varies with changes in these quantities

2.17 coverage factor
number by which a standard measurement uncertainty of a measurement result is multiplied to obtain an expanded measurement uncertainty

2.18 expanded measurement uncertainty, expanded uncertainty
half-width of a symmetric coverage interval, centered around the estimate of a quantity, with a specified coverage probability

2.19 coverage interval
interval of values which can be attributed to a quantity and, based on the available information, is associated with a stated high probability

2.20 coverage probability
probability associated with a coverage interval

2.21 target measurement uncertainty, target uncertainty
measurement uncertainty formulated as a goal and decided on the basis of a specified intended use of measurement results

2.22 calibration of a measuring system, calibration
definition (a)
operation establishing the relation between quantity values provided by measurement standards and the corresponding indications of a measuring system, carried out under specified conditions and including evaluation of measurement uncertainty
definition (b)
operation that establishes the relation, obtained by reference to one or more measurement standards, that exists under specified conditions, between the indication of a measuring system and the measurement result that would be obtained using the measuring system

2.23 calibration hierarchy
sequence of calibrations of measuring systems between a stated metrological reference and the final measuring system

2.24 metrological traceability
property of a measurement result relating the result to a stated metrological reference through an unbroken chain of calibrations of a measuring system or comparisons, each contributing to the stated measurement uncertainty

2.25 metrological traceability chain, traceability chain
chain of alternating measuring systems with associated measurement procedures and measurement standards, from a measurement result to a stated metrological reference

2.26 metrological traceability to a measurement unit, metrological traceability to a unit
metrological traceability of a measurement result to the definition of a measurement unit through a stated metrological traceability chain

2.27 verification
confirmation through examination of a given item and provision of objective evidence that it fulfils specified requirements
[modified from ISO 9000:2000, item 3.8.4]

2.28 validation
confirmation through examination of a given item and provision of objective evidence that it fulfils the requirements for a stated intended use
[modified from ISO 9000:2000, item 3.8.5]

2.29 comparability of measurement results, comparability
property of measurement results enabling them to be compared because they are metrologically traceable to the same stated metrological reference

2.30 compatibility of measurement results, compatibility
property satisfied by all the measurement results of the same quantity, characterized by an adequate overlap of their corresponding sets of quantity values

2.31 influence quantity
quantity which, in a direct measurement, is neither the measurand nor the quantity being measured, but whose change affects the relation between the indication of the measuring system and the measurement result

2.32 correction
modification applied to a quantity value obtained from measurement, to compensate for a systematic effect

2.33 measurement function
function expressing the mathematical relation between one or more measurands and the quantity or quantities that must be measured, or whose values can be otherwise obtained, to calculate a value of each measurand

2.34 input quantity to a measurement function
quantity that must be measured, or whose value can be otherwise obtained, to calculate a value of a measurand as an output of the measurement function

2.35 measurement precision, precision
closeness of agreement between quantity values obtained by replicate measurements of a quantity, under specified conditions

2.36 repeatability condition of measurement, repeatability condition
condition of measurement in a set of conditions including the same measurement procedure, same operator, same measuring system, same operating conditions and same location, and replicated measurements over a short period of time

2.37 measurement repeatability, repeatability
measurement precision under repeatability conditions of measurement

2.38 intermediate precision condition of measurement, intermediate precision condition
condition of measurement in a set of conditions including the same measurement procedure, same location, and replicated measurements over an extended period of time

2.39 intermediate measurement precision, intermediate precision
measurement precision under intermediate precision conditions of measurement

2.40 reproducibility condition of measurement, reproducibility condition
condition of measurement in a set of conditions including different locations, operators, and measuring systems

2.41 measurement reproducibility, reproducibility
measurement precision under reproducibility conditions of measurement

2.42 (preliminary definition) selectivity of a measuring system, selectivity
capability of a measuring system, using a specified measurement procedure, to provide measurement results for two or more quantities of the same kind involving different components in a system undergoing measurement, without interference from each other or from other quantities in the same system
capability of a measuring system to provide a measurement result for a given quantity in the presence of other quantities of the same kind in the system undergoing measurement

2.43 (preliminary definition) specificity of a measuring system, specificity
capability of a measuring system, using a specified measurement procedure, to provide a measurement result for a quantity involving a specified component in a system undergoing measurement, without interference from other components in the same system

Chapter 3: DEVICES FOR MEASUREMENT

This Chapter defines only a selection of important concepts. Further concepts are found in IEC 60050.

3.1 measuring instrument
device or combination of devices designed for measurement of quantities

3.2 material measure
device reproducing or supplying, in a permanent manner during its use, quantities of given kinds, each with an assigned value

3.3 measuring transducer
device that provides at its output a quantity having a determined relation to the quantity at its input

3.4 measuring chain
series of elements of a measuring system constituting one single path of the measurement signal

3.5 measuring system, measurement system
set of measuring instruments and other devices or substances assembled and adapted to the measurement of quantities of specified kinds within specified intervals of values

3.6 indicating measuring instrument
measuring instrument providing an output signal carrying information about the value of the quantity to be measured

3.7 displaying device
device providing the indication of a measuring system in visual form

3.8 sensor
element of a measuring system that is directly affected by the phenomenon, body, or substance carrying the quantity to be measured

3.9 detector
device or substance that indicates the presence of a phenomenon, body, or substance when a threshold value of an associated quantity is exceeded

3.10 scale of a displaying device, scale
part of a displaying device consisting of an ordered set of marks, together with any associated numbers or quantity values

3.11 adjustment of a measuring system, adjustment
set of operations carried out on a measuring system in order that it provide prescribed indications corresponding to given values of the quantity to be measured

3.12 zero adjustment of a measuring system, zero adjustment
adjustment of a measuring system providing a null indication corresponding to a null value of the quantity to be measured

Chapter 4: CHARACTERISTICS OF MEASURING SYSTEMS

4.1 indication of a measuring system, indication
quantity value provided as the output of a measuring system

4.2 indication interval
set of quantity values bounded by the extreme possible indications of a measuring system

4.3 nominal indication interval, nominal interval
set of quantity values, bounded by rounded or approximate extreme indications obtainable with a particular setting of the controls of a measuring system and used to designate this setting

4.4 span of a nominal interval, span
absolute value of the difference between the extreme quantity values of a nominal indication interval

4.5 nominal quantity value, nominal value
rounded or approximate quantity value of a characteristic of a measuring system that provides a guide to its use

4.6 measuring interval, working interval
set of values of the quantities of the same kind that can be measured by a given measuring system, with specified measurement uncertainty under defined conditions

4.7 steady state condition for a measuring system, steady state condition
operating condition of a measuring system in which the possible variation with time of the quantity being measured is such that a calibration of the measuring system carried out with a measurand constant with time remains valid

4.8 rated operating condition for a measuring system, rated operating condition
condition that must be fulfilled during measurement in order that a measuring system perform as designed

4.9 limiting condition for a measuring system, limiting condition
extreme condition that a measuring system is required to withstand without damage, and without degradation of specified metrological characteristics when it is subsequently operated under its rated operating conditions

4.10 reference condition for a measuring system, reference condition
condition of use prescribed for evaluating the performance of a measuring system or for comparison of measurement results

4.11 optimum condition for a measuring system, optimum condition
condition of use for a measuring system, under which its contribution to measurement uncertainty is minimum

4.12 sensitivity of a measuring system, sensitivity
quotient of the change in the indication of a measuring system and the corresponding change in the value of the quantity being measured

4.13 resolution of a measuring system
smallest change, in the value of a quantity being measured by a measuring system, that causes a perceptible change in the corresponding indication

4.14 resolution of a displaying device
smallest difference between indications of a displaying device that can be meaningfully distinguished

4.15 discrimination threshold
largest change in the value of a quantity being measured by a measuring system that causes no detectable change in the corresponding indication

4.16 dead band of a measuring system, dead band
maximum interval through which the value of a quantity being measured by a measuring system can be changed in both directions without producing a detectable change in the corresponding indication

4.17 stability of a measuring system, stability
ability of a measuring system to maintain its metrological characteristics constant with time

4.18 drift of a measuring system, drift
change in the indication of a measuring system, generally slow and continuous, related neither to a change in the quantity being measured nor to a change of an influence quantity

4.19 variation due to an influence quantity
difference between the indications of a measuring system for the same value of the quantity being measured when an influence quantity assumes, successively, two different values

4.20 step-change response time of a measuring system, step-change response time
duration between the instant when a quantity value at the input of a measuring system is subjected to a step change between two specified steady states and the instant when the corresponding indication settles within specified limits around its final steady value

4.21 repeatability of a measuring system, repeatability
property of a measuring system to provide closely similar indications for replicated measurements of the same quantity under repeatability conditions

4.22 instrumental uncertainty
component of measurement uncertainty attributed to a measuring instrument and determined by its calibration

4.23 accuracy class
class of measuring instruments that meet stated metrological requirements which are intended to keep instrumental uncertainty within specified limits under specified operating conditions

Chapter 5: MEASUREMENT STANDARDS, ETALONS

In science and technology, the English word “standard” is used with two different meanings: as a widely adopted written standard, specification, technical recommendation or similar document (in French “norme”) and as a measurement standard (in French “étalon”). This Vocabulary is concerned solely with the second meaning.

5.1 measurement standard, standard, etalon
realization of the definition of a given quantity, with stated value and measurement uncertainty, used as a reference

5.2 national measurement standard, national standard
measurement standard designated as a national stated metrological reference

5.3 primary measurement standard, primary standard
measurement standard whose quantity value and measurement uncertainty are established without relation to another measurement standard for a quantity of the same kind

5.4 secondary measurement standard, secondary standard
measurement standard whose quantity value and measurement uncertainty are assigned through calibration against, or comparison with, a primary measurement standard for a quantity of the same kind

5.5 reference measurement standard, reference standard
measurement standard used for the calibration of working measurement standards in a given organization or at a given location

5.6 working measurement standard, working standard
measurement standard that is used routinely to calibrate, verify, or check measuring systems, material measures, or reference materials

5.7 travelling measurement standard, travelling standard
measurement standard, sometimes of special construction, intended for transport between
different locations

5.8 transfer measurement device, transfer device
measurement device used as an intermediary to compare measurement standards

5.9 intrinsic measurement standard, intrinsic standard
measurement standard based on a sufficiently stable and reproducible property of a phenomenon or substance

5.10 check measurement device, check device
measurement device used routinely for verifying the functioning of a measuring system

5.11 conservation of a measurement standard
operation or set of operations necessary to preserve the metrological properties of a measurement standard within stated limits

5.12 calibrator
measurement standard used in the calibration of a measuring system

5.13 reference material, RM
material, sufficiently homogeneous and stable with respect to one or more specified quantities, used for the calibration of a measuring system, or for the assessment of a measurement procedure, or for assigning values and measurement uncertainties to quantities of the same kind for other materials

5.14 certified reference material, CRM
reference material, accompanied by an authenticated certificate, having for each specified quantity a value, measurement uncertainty, and stated metrological traceability chain

5.15 commutability of a reference material
property of a given reference material demonstrated by the closeness of agreement between the relation among the measurement results, for a stated quantity in this material, obtained according to two given measurement procedures, and the relation obtained among the measurement results for other specified materials

5.16 reference data
data that is critically evaluated and verified, obtained from an identified source, and related to a property of a phenomenon, body, or substance, or a system of components of known composition or structure

5.17 standard reference data
reference data issued by a stated recognized authority

5.18 reference quantity value, reference value
quantity value, generally accepted as having a suitably small measurement uncertainty, to be used as a basis for comparison with values of quantities of the same kind

Annex A: CONCEPTS USED IN THE CLASSICAL APPROACH (CA) TO MEASUREMENT

A1 true value of a quantity, true value
quantity value consistent with the definition of a quantity

A2 accuracy of measurement, accuracy
closeness of agreement between a quantity value obtained by measurement and the true value of the measurand

A3 accuracy of a measuring system, accuracy
ability of a measuring system to provide a quantity value close to the true value of a measurand

A4 trueness of measurement, trueness
closeness of agreement between the average that would ensue from an infinite number of quantity values obtained under specified measurement conditions and the true value of the measurand

A5 error of measurement, error
difference of quantity value obtained by measurement and true value of the measurand

A6 error of indication
difference of indication of a measuring system and true value of the measurand

A7 random error of measurement, random error
difference of quantity value obtained by measurement and average that would ensue from an infinite number of replicated measurements of the same measurand carried out under repeatability conditions

A.8 systematic error of measurement, systematic error
difference of average that would ensue from an infinite number of replicated measurements of the same measurand carried out under repeatability conditions and true value of the measurand

A9 accuracy class
class of measuring instruments that meet stated metrological requirements which are intended to keep errors of indication within specified limits under specified operating conditions

A10 maximum permissible error, limit of error
one of the two extreme values of the error of indication permitted by specifications or regulations for a given measuring system

A11 datum error of a measuring system, datum error
error of indication of a measuring system at a specified indication or a specified value of the measurand

A12 zero error of a measuring system, zero error
datum error for zero value of the measurand

A13 intrinsic error of a measuring system, intrinsic error
error of indication when determined under reference conditions

A14 bias of a measuring system, bias
systematic error of indication of a measuring system

Annexe B CONCEPT DIAGRAMS

Figure B1: Concept Diagram for Part of Chapter1, Centred on "quantity"


Figure B2: Concept Diagram for Part of Chapter1, Centred on "unit"