The permitted range for a characteristic, given as limits around a nominal value, such as ±0.5 % of reading for a pressure gauge or 25.000 ± 0.005 mm for a bore. In calibration the tolerance usually comes from the manufacturer's spec, a customer requirement or a regulation, and it is what as-found and as-left data are judged against. Tolerance is set by need while uncertainty is set by the measurement, and the ratio between them decides how confidently a call can be made.
Tolerance on this transmitter is 0.25 percent of span and our uncertainty there is 0.05, so we've got 5 to 1.
Also heard as
- tol
- spec limit
- tolerance limit
Do not mix it up with
- Uncertainty: Tolerance is how far the item is allowed to deviate; uncertainty is how well the lab can measure that deviation.
Related terms
Guard band
A margin that pulls acceptance limits inside the tolerance limits to cut the risk of passing nonconforming items.
TUR
Test uncertainty ratio, the tolerance being checked divided by the expanded uncertainty of the measurement process.
MPE
Maximum permissible error: the error limit an instrument must stay inside to conform, set by its spec, a standard or the law.
Decision rule
The agreed method for factoring measurement uncertainty into a pass or fail call against a spec.
OOT
Out of tolerance, an as-found calibration result outside the instrument's allowed limits.