Dictionary · Uncertainty
Definitional uncertainty
The component of uncertainty resulting from the finite detail in the definition of the measurand itself — the floor below which no better procedure can go without redefining the quantity.
Related terms
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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
Expanded measurement uncertainty
The product of a combined standard uncertainty and a coverage factor greater than one: U = k·u꜀. With k = 2 the coverage probability is about 95 % for a normal distribution.
VIM (JCGM 200:2012) 2.35
Rectangular distribution
A probability distribution assigning equal likelihood everywhere between limits ±a. Used for Type B components where only limits are known; its standard uncertainty is a/√3.
GUM (JCGM 100:2008) 4.3.7
Input quantity in a measurement model
A quantity that must be measured, or whose value can be otherwise obtained, to calculate a measured value of the measurand.
VIM (JCGM 200:2012) 2.50
Standard measurement uncertainty
Measurement uncertainty expressed as a standard deviation, denoted u — the common currency into which all components are converted before combination.
VIM (JCGM 200:2012) 2.30
Measurement model
The mathematical relation among all quantities known to be involved in a measurement, of the general form f(Y, X₁, …, Xₙ) = 0.
VIM (JCGM 200:2012) 2.48