Inspection Fundamentals and Terminology
Inspection is the planned comparison of a characteristic against a stated requirement, and every inspection question can be broken into four parts: the characteristic, the requirement, the measurement method, and the decision rule. Master the vocabulary. Accuracy is closeness to the true value; precision is repeatability of repeated readings. A gauge can be precise and inaccurate (a consistent offset). Tolerance is the allowed range; specification limits bound it; the tolerance zone is the span between limits. Nominal is the design value, not an acceptance limit. Attribute inspection judges conform/nonconform (go/no-go); variable inspection produces a number on a scale. Confuse these and the sampling and uncertainty questions collapse.
Other terms candidates must own: true position, MMC/LMC (maximum/least material condition), allowance versus clearance, bias (systematic) versus random error, and resolution (smallest readable increment). Traceability means an unbroken chain of calibrations to a reference standard. Conformity is a decision, not a measurement.
Traps: (1) Treating precision as accuracy. (2) Assuming a reading inside tolerance proves the part is good - measurement uncertainty can flip a marginal call. (3) Mixing MMC (largest pin/smallest hole) with LMC. (4) Believing a go/no-go gauge reports a value; it reports only pass/fail.
Rule of thumb (the 10:1 or 4:1 gauge rule): the measurement equipment's uncertainty should be no more than about one-tenth (tight) or at most one-fourth (common practice) of the tolerance being verified. Worked example: tolerance ±0.10 mm (0.20 mm total). A gauge with 0.05 mm uncertainty consumes 25% of tolerance - acceptable under the 4:1 rule, marginal under 10:1, so flag it and consider better equipment or guard-banding.