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Showing 1591–1620 of 1709 reference entries

PhysicsSpecular and diffuse reflection

Reflection angles are measured from the local normal.

ModelPhysicsTotal internal reflection and evanescent fields

Total reflected flux does not mean zero field beyond the interface.

ModelPhysicsSpherical-mirror images and signs

A virtual image is formed by ray extensions, not actual ray convergence.

ModelPhysicsPhotoelectric threshold and stopping potential

Photon frequency sets maximum photoelectron energy in the single-photon model.

ModelPhysicsDe Broglie wavelength and particle momentum

A momentum state has a spatial wave phase.

ModelMeasurementQuantity kind and physical dimension

Equal dimensions do not make quantities interchangeable.

DefinitionMeasurementQuantity value, numerical value and unit

A numerical value depends on the chosen unit.

DefinitionMeasurementCoherent derived units

Coherence means no extra numerical factor in the base-unit product.

DefinitionMeasurementOrdinal quantities and nominal properties

Ordering and category labels do not justify ordinary arithmetic.

DefinitionMeasurementMeasurement principle, method and procedure

A physical phenomenon, an approach and a detailed procedure have different roles.

DefinitionMeasurementMeasuring instrument and measuring system

A complete measurement system can include more than one device.

DefinitionMeasurementSensor, transducer and detector

Component names describe different measurement roles.

DefinitionMeasurementInstrument indication and measurement result

A displayed reading is only one part of a measurement result.

DefinitionMeasurementAdjustment, calibration and zero adjustment

Changing an instrument response differs from determining its calibration.

DefinitionMeasurementReference and conventional quantity values

An accepted comparison value need not be an exact true value.

DefinitionMeasurementIndication interval, measuring interval and span

Possible readings differ from a validated interval of measurement.

DefinitionMeasurementRated operating conditions

Instrument properties are specified within a domain of use.

DefinitionMeasurement · ChemistrySelectivity of a measuring system

Responding to a target differs from excluding interference.

DefinitionMeasurementDiscrimination threshold and dead band

An undetected input change differs from an interval with no output change.

DefinitionMeasurementStability of a measuring instrument

Time stability differs from short-term repeatability.

DefinitionMeasurementMaximum permissible error and accuracy class

A specification limit is not an uncertainty estimate.

DefinitionMeasurementDefinitional uncertainty

More repetitions do not resolve an underspecified measurand.

DefinitionMeasurementRelative standard uncertainty

Relative uncertainty uses a nonzero measured magnitude.

DefinitionMeasurementBlank indications and null measurement uncertainty

A zero or blank reading can still have uncertainty.

DefinitionMeasurementTarget measurement uncertainty

An intended-use target differs from achieved uncertainty.

DefinitionMeasurementIntermediate precision conditions

Within-location changed conditions differ from strict repeatability.

DefinitionMeasurementCommutability of a reference material

Certification alone does not establish equivalence across procedures.

DefinitionChemistrySubstances, elements, compounds and mixtures

Chemical composition and spatial uniformity describe different features of matter.

DefinitionChemistryPhysical change and chemical change

A change of phase need not change chemical identity.

DefinitionChemistryEmpirical, molecular and structural formulas

A formula's subscripts represent different information in different chemical models.

Definition
DefinitionSource checked

Reference and conventional quantity values

Measurement

An accepted comparison value need not be an exact true value.

Key knowledge

A reference quantity value is used as a basis for comparison with values of quantities of the same kind. A conventional quantity value is attributed by agreement for a given purpose. A reference can be a conventional value or another specified value with associated uncertainty. Agreement does not make a value an exact property of nature, and finite detail in a measurand definition can allow more than one value consistent with that definition.

Conditions and scope

  • State the quantity kind, convention, reference provenance, purpose and any relevant uncertainty.
  • Do not treat a historical conventional electrical-unit example as the current SI definition; a negligible-reference-uncertainty approximation needs justification for the comparison.
Sources · 3

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. International Vocabulary of Metrology (VIM3)Joint Committee for Guides in Metrology (JCGM)Reference guideVIM3, entry 5.18VIM3, entry 2.12VIM3, entry 2.11jcgm.bipm.org

Evidence and review

Read VIM5.18 reference-value definition/notes,2.12 conventional-value definition/notes and2.11 true-value definition/finite-measurand-detail note. Exclude historical electrical conventional constants as current SI realizations.

2026-10-10 · /root/audit_life_earth_chemistry — independent Chemistry/Life/Earth editor. Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–3 of 3 relationships

Scientific relationships · 3 / 3

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 3

    Linked statements

    • A reference quantity value is used as a basis for comparison with values of quantities of the same kind. A conventional quantity value is attributed by agreement for a given purpose. A reference can be a conventional value or another specified value with associated uncertainty. Agreement does not make a value an exact property of nature, and finite detail in a measurand definition can allow more than one value consistent with that definition.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

  2. Related to
    Relationship sources · 3

    Linked statements

    • A reference quantity value is used as a basis for comparison with values of quantities of the same kind. A conventional quantity value is attributed by agreement for a given purpose. A reference can be a conventional value or another specified value with associated uncertainty. Agreement does not make a value an exact property of nature, and finite detail in a measurand definition can allow more than one value consistent with that definition.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

  3. Related to
    Relationship sources · 3

    Linked statements

    • A reference quantity value is used as a basis for comparison with values of quantities of the same kind. A conventional quantity value is attributed by agreement for a given purpose. A reference can be a conventional value or another specified value with associated uncertainty. Agreement does not make a value an exact property of nature, and finite detail in a measurand definition can allow more than one value consistent with that definition.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

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Foundational reference additions