S = number stages, integer satisfying S³2
ni = sample sizes, real numbers satisfying ni>0
ai = accept numbers, integers satisfying ai³ai-1 where a0=-1. Entering a # sign is interpreted as -1.
ri = reject numbers, integers satisfying ri³ri-1 where r0=1 and ri³ai+2 except rS=aS+1
Units of measure for ni = length, area, volume or some other quantity of material
Procedure:
(1) Take a representative sample of size n1 from the lot to be inspected.
(2) Count the number of defects in this sample.
(3) If this count is less than or equal to a1, accept the lot.
(4) If this count is greater than or equal to r1, reject the lot.
(5) Otherwise, set i=2.
(6) Take an additional representative sample of size ni from the lot.
(7) Count the total number of defects in the combined sample of size n1+...+ni.
(8) If this count is less than or equal to ai, accept the lot.
(9) If this count is greater than or equal to ri, reject the lot.
(10) Otherwise, increase i by 1 and go back to step 6.
This procedure always terminates on the S-th stage because of the restriction rS=aS+1.
Sometimes the accept or reject decision is determined before all units are inspected. In this case, the inspection can be curtailed. For multiple sampling plans for defects you can curtail on rejection only during any stage as follows:
Curtail on Rejection during i-th Stage: Stop the inspection and reject as soon as ri defective units are found.