A decision rule in which the measured value alone is compared with the tolerance limits: inside is a pass, outside is a fail. The uncertainty still exists and the risk of a wrong call near the limits approaches 50 %, so the rule is usually paired with a requirement that the uncertainty be small relative to the tolerance, such as a TUR of 4:1 or better. Supplier and customer share the risk of wrong calls at the edges.
Customer wants simple acceptance, so a 9.99 on a 10.00 limit is a pass even with our uncertainty.
Also heard as
- shared risk
- zero guard band
Do not mix it up with
- Guard band: Guard banding moves the pass line inside the tolerance; simple acceptance keeps the pass line on the tolerance limit.
Related terms
Decision rule
The agreed method for factoring measurement uncertainty into a pass or fail call against a spec.
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.
PFA
Probability of false accept, the chance that a nonconforming item is measured and passed as good.
Specific risk
The probability that one particular measured item is out of tolerance, given its actual measured value.