Ten VIM terms every calibration user should know
Measurand, indication, error, correction, accuracy, precision, trueness, resolution, drift and traceability — defined as the international vocabulary defines them.
- Measurand: the quantity intended to be measured — e.g. the air temperature at a defined location, not 'the thermometer reading'.
- Indication: the value provided by the instrument.
- Measurement error: measured value minus a reference value; only estimable.
- Correction: the compensation for an estimated systematic error, applied to an indication.
- Accuracy: closeness of agreement between a measured value and the true value — a qualitative concept.
- Trueness: closeness of the average of many measurements to the true value; related to systematic error.
- Precision: closeness of agreement between repeated measurements; related to random error.
- Resolution: the smallest change in the quantity that causes a perceptible change in the indication.
- Instrumental drift: continuous change in indication over time due to changes in metrological properties.
- Metrological traceability: relation to a reference through a documented unbroken chain of calibrations, each contributing uncertainty.
Using these words as the VIM defines them removes most arguments about what a certificate or specification actually claims.
Frequently asked questions
- Is 'accuracy ±0.1 °C' on a datasheet an uncertainty?
- No. It is usually a maximum permissible error under stated conditions. Treat it as a Type B limit, not as an expanded uncertainty.
References
- [1]JCGM 200:2012 — International vocabulary of metrology (VIM), 3rd edition
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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