Measurement uncertainty puts a size on the doubt left in a result once every known correction is applied, drawing on repeat data, certificates, specs and judgment. It is expressed either as a standard deviation (standard uncertainty) or as the half-width of an interval at a stated coverage probability (expanded uncertainty). It has no sign, it never reaches zero, and it must be stated before a result can be compared with a tolerance or with another lab.
Reading is fine, but the uncertainty on that point is 0.8 µm and the tolerance is only 1 µm, so we can't call it.
Also heard as
- measurement uncertainty
- MU
Do not mix it up with
Related terms
Error
The signed difference between a measured value and the reference value of the quantity being measured.
Standard uncertainty
Uncertainty expressed as one standard deviation, the common currency for combining uncertainty components.
Expanded uncertainty
Combined standard uncertainty multiplied by a coverage factor to give an interval with a stated coverage probability.
Uncertainty budget
A table listing every uncertainty source in a measurement with its size, distribution, divisor and contribution to the total.