Knowledge
Metrology Dictionary
The complete VIM vocabulary — all numbered concepts of JCGM 200:2012 as faithful paraphrases with clause citations — plus clearly labeled practice terms from the GUM, ILAC, ISO and NIST guidance.
Target measurement uncertainty
An uncertainty specified in advance as an upper limit, decided from the intended use of the result.
VIM (JCGM 200:2012) 2.34 · Uncertainty
Test accuracy ratio (TAR)
The legacy ratio of unit-under-test tolerance to the accuracy specification of the standard used. Superseded in rigorous work by the test uncertainty ratio, which accounts for the whole measurement process.
Industry practice · Quality & Accreditation
Test uncertainty ratio (TUR)
The ratio of the tolerance of the unit under test to the expanded uncertainty of the measurement process used to test it. A 4:1 TUR is the traditional benchmark; lower ratios call for guard banding or risk analysis (ANSI/NCSL Z540.3).
ANSI/NCSL Z540.3 · Quality & Accreditation
Thermal expansion (dimensional)
The length change of a body with temperature, characterized by its coefficient of linear expansion. Dimensional results are reported at the standard reference temperature of 20 °C defined by ISO 1.
ISO 1:2022 · Dimensional
Transfer measurement device
A device used as an intermediary to compare measurement standards — transferring, not holding, the quantity value.
VIM (JCGM 200:2012) 5.9 · Standards & Units
Travelling measurement standard
A standard, sometimes of special construction, intended for transport between locations — the artifacts that carry interlaboratory comparisons.
VIM (JCGM 200:2012) 5.8 · Standards & Units
Triangular distribution
A probability distribution rising linearly to a peak midway between limits ±a. Used when values near the centre are more likely; its standard uncertainty is a/√6.
GUM (JCGM 100:2008) 4.3.9 · Uncertainty
True quantity value
The quantity value consistent with the definition of the quantity. In practice unknowable; measurement estimates it with stated uncertainty.
VIM (JCGM 200:2012) 2.11 · General
Type A evaluation of measurement uncertainty
Evaluation of a component of uncertainty by statistical analysis of measured values obtained under defined conditions — e.g. the standard deviation of the mean of repeated readings.
VIM (JCGM 200:2012) 2.28 · Uncertainty
Type B evaluation of measurement uncertainty
Evaluation of a component of uncertainty by means other than statistical analysis of current measurements — calibration certificates, specifications, handbook data, assumed distributions.
VIM (JCGM 200:2012) 2.29 · Uncertainty