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Attribute sampling draws a sample whose size grows with the square root of lot size, scaled by inspection level, and accepts the lot if defects found do not exceed the acceptance number derived from the AQL. Tightened inspection uses larger samples, reduced inspection smaller ones, which is how switching rules reward or punish supplier history.
Sample size
Sample = sqrt(lot size) x level factor (I 0.4, II 1.0, III 1.6)
Acceptance
Acceptance number = floor(sample size x AQL % / 100); accept if defects <= acceptance number
Sampling plans used for contractual or regulatory acceptance must follow the published standard tables and switching rules. Use this as a planning approximation only.
It approximates them. For contractual or regulatory acceptance always use the actual code letter and table from the applicable standard rather than an approximation.
No. AQL is the quality level a sampling plan will routinely accept, not a target. Producing at AQL guarantees regular rejections, because the plan is designed to accept better-than-AQL lots.