EXAMPLE 1 1 kg mass measurement standard with an associated standard measurement uncertainty of 3 µg.
EXAMPLE 2 100 Ω measurement standard resistor with an associated standard measurement uncertainty of 1 µΩ.
EXAMPLE 3 Caesium frequency standard with a relative standard measurement uncertainty of 2 × 10−15.
EXAMPLE 4 Hydrogen reference electrode with an assigned quantity value of 7.072 and an associated standard measurement uncertainty of 0.006.
EXAMPLE 5 Set of reference solutions of cortisol in human serum having a certified quantity value with measurement uncertainty for each solution.
EXAMPLE 6 Reference material providing quantity values with measurement uncertainties for the mass concentration of each of ten different proteins.
NOTE 1 A “realization of the definition of a given quantity” can be provided by a measuring system, a material measure, or a reference material.
NOTE 2 A measurement standard is frequently used as a reference in establishing measured quantity values and associated measurement uncertainties for other quantities of the same kind, thereby establishing metrological traceability through calibration of other measurement standards, measuring instruments, or measuring systems.
NOTE 3 The term “realization” is used here in the most general meaning. It denotes three procedures of “realization”. The first one consists in the physical realization of the measurement unit from its definition and is realization sensu stricto. The second, termed “reproduction”, consists not in realizing the measurement unit from its definition but in setting up a highly reproducible measurement standard based on a physical phenomenon, as it happens, e.g. in case of use of frequency‑stabilized lasers to establish a measurement standard for the metre, of the Josephson effect for the volt or of the quantum Hall effect for the ohm. The third procedure consists in adopting a material measure as a measurement standard. It occurs in the case of the measurement standard of 1 kg.
NOTE 4 A standard measurement uncertainty associated with a measurement standard is always a component of the combined standard measurement uncertainty (see GUM:1995, 2.3.4) in a measurement result obtained using the measurement standard. Frequently, this component is small compared with other components of the combined standard measurement uncertainty.
NOTE 5 Quantity value and measurement uncertainty must be determined at the time when the measurement standard is used.
NOTE 6 Several quantities of the same kind or of different kinds may be realized in one device which is commonly also called a measurement standard.
NOTE 7 The word “embodiment” is sometimes used in the English language instead of “realization”.
NOTE 8 In science and technology, the English word “standard” is used with at least two different meanings: as a specification, technical recommendation, or similar normative document (in French “norme”) and as a measurement standard (in French “étalon”). This Vocabulary is concerned solely with the second meaning.
NOTE 9 The term “measurement standard” is sometimes used to denote other metrological tools, e.g. ‘software measurement standard’ (see ISO 5436‑2).
EXAMPLE 1 The international prototype of the kilogram.
EXAMPLE 2 Chorionic gonadotrophin, World Health Organization (WHO) 4th international standard 1999, 75/589, 650 International Units per ampoule.
EXAMPLE 3 VSMOW2 (Vienna Standard Mean Ocean Water) distributed by the International Atomic Energy Agency (IAEA) for differential stable isotope amount‑of‑substance ratio measurements.
EXAMPLE 1 Primary measurement standard of amount‑of‑substance concentration prepared by dissolving a known amount of substance of a chemical component to a known volume of solution.
EXAMPLE 2 Primary measurement standard for pressure based on separate measurements of force and area.
EXAMPLE 3 Primary measurement standard for isotope amount‑of‑substance ratio measurements, prepared by mixing known amount‑of‑substances of specified isotopes.
EXAMPLE 4 Triple‑point‑of‑water cell as a primary measurement standard of thermodynamic temperature.
EXAMPLE 5 The international prototype of the kilogram as an artifact, chosen by convention.
NOTE 1 Calibration may be obtained directly between a primary measurement standard and a secondary measurement standard, or involve an intermediate measuring system calibrated by the primary measurement standard and assigning a measurement result to the secondary measurement standard.
NOTE 2 A measurement standard having its quantity value assigned by a ratio primary reference measurement procedure is a secondary measurement standard.
NOTE 1 A working measurement standard is usually calibrated with respect to a reference measurement standard.
NOTE 2 In relation to verification, the terms “check standard” or “control standard” are also sometimes used.
EXAMPLE Portable battery‑operated caesium‑133 frequency measurement standard.
NOTE Sometimes, measurement standards are used as transfer devices.
EXAMPLE 1 Triple‑point‑of‑water cell as an intrinsic measurement standard of thermodynamic temperature.
EXAMPLE 2 Intrinsic measurement standard of electric potential difference based on the Josephson effect.
EXAMPLE 3 Intrinsic measurement standard of electric resistance based on the quantum Hall effect.
EXAMPLE 4 Sample of copper as an intrinsic measurement standard of electric conductivity.
NOTE 1 A quantity value of an intrinsic measurement standard is assigned by consensus and does not need to be established by relating it to another measurement standard of the same type. Its measurement uncertainty is determined by considering two components: the first associated with its consensus quantity value and the second associated with its construction, implementation, and maintenance.
NOTE 2 An intrinsic measurement standard usually consists of a system produced according to the requirements of a consensus procedure and subject to periodic verification. The consensus procedure may contain provisions for the application of corrections necessitated by the implementation.
NOTE 3 Intrinsic measurement standards that are based on quantum phenomena usually have outstanding stability.
NOTE 4 The adjective “intrinsic” does not mean that such a measurement standard may be implemented and used without special care or that such a measurement standard is immune to internal and external influences.
NOTE Conservation commonly includes periodic verification of predefined metrological properties or calibration, storage under suitable conditions, and specified care in use.
NOTE The term “calibrator” is only used in certain fields.
NOTE 1 Examination of a nominal property provides a nominal property value and associated uncertainty. This uncertainty is not a measurement uncertainty.
NOTE 2 Reference materials with or without assigned quantity values can be used for measurement precision control whereas only reference materials with assigned quantity values can be used for calibration or measurement trueness control.
NOTE 3 ‘Reference material’ comprises materials embodying quantities as well as nominal properties.
EXAMPLE 1 Examples of reference materials embodying quantities:
EXAMPLE 2 Examples of reference materials embodying nominal properties:
NOTE 4 A reference material is sometimes incorporated into a specially fabricated device.
EXAMPLE 1 Substance of known triple‑point in a triple‑point cell.
EXAMPLE 2 Glass of known optical density in a transmission filter holder.
EXAMPLE 3 Spheres of uniform size mounted on a microscope slide.
NOTE 5 Some reference materials have assigned quantity values that are metrologically traceable to a measurement unit outside a system of units. Such materials include vaccines to which International Units (IU) have been assigned by the World Health Organization.
NOTE 6 In a given measurement, a given reference material can only be used for either calibration or quality assurance.
NOTE 7 The specifications of a reference material should include its material traceability, indicating its origin and processing (Accred. Qual. Assur.:2006)[45].
NOTE 8 ISO/REMCO has an analogous definition[45] but uses the term “measurement process” to mean ‘examination’ (ISO 15189:2007, 3.4), which covers both measurement of a quantity and examination of a nominal property.
Human serum with assigned quantity value for the concentration of cholesterol and associated measurement uncertainty stated in an accompanying certificate, used as a calibrator or measurement trueness control material.
NOTE 1 ‘Documentation’ is given in the form of a ‘certificate’ (see ISO Guide 31:2000).
NOTE 2 Procedures for the production and certification of certified reference materials are given, e.g. in ISO Guide 34 and ISO Guide 35.
NOTE 3 In this definition, “uncertainty” covers both ‘measurement uncertainty’ and ‘uncertainty associated with the value of a nominal property’, such as for identity and sequence. “Traceability” covers both ‘metrological traceability of a quantity value’ and ‘traceability of a nominal property value’.
NOTE 4 Specified quantity values of certified reference materials require metrological traceability with associated measurement uncertainty (Accred. Qual. Assur.:2006)[45].
NOTE 5 ISO/REMCO has an analogous definition (Accred. Qual. Assur.:2006)[45] but uses the modifiers ‘metrological’ and ‘metrologically’ to refer to both quantity and nominal property.
NOTE 1 The reference material in question is usually a calibrator and the other specified materials are usually routine samples.
NOTE 2 The measurement procedures referred to in the definition are the one preceding and the one following the reference material (calibrator) in question in a calibration hierarchy (see ISO 17511).
NOTE 3 The stability of commutable reference materials is monitored regularly.
EXAMPLE Reference data for solubility of chemical compounds as published by the IUPAC.
NOTE 1 In this definition, accuracy covers, for example, measurement accuracy and ‘accuracy of a nominal property value’.
NOTE 2 “Data” is a plural form, “datum” is the singular. “Data” is commonly used in the singular sense, instead of “datum”.
EXAMPLE 1 Values of the fundamental physical constants, as regularly evaluated and published by ICSU CODATA.
EXAMPLE 2 Relative atomic mass values, also called atomic weight values, of the elements, as evaluated every two years by IUPAC‑CIAAW at the IUPAC General Assembly and published in Pure Appl. Chem. or in J. Phys. Chem. Ref. Data.
NOTE 1 A reference quantity value can be a true quantity value of a measurand, in which case it is unknown, or a conventional quantity value, in which case it is known.
NOTE 2 A reference quantity value with associated measurement uncertainty is usually provided with reference to