Selection of samples.

§ 42.131 Selection of samples. (a) Prior to commencement of on-line sampling and inspection, the total amount of production for a given day or shift is predicted and is then subdivided into conveniently designated portions of production approximately equal in size. Portions may be designated by sequential numbers (e.g., containers 1 through 500 are portion 1, containers 501 through 1000 are portion 2, etc.) or by time intervals (e.g., the first half hour of production is portion 1, the second half hour of production is portion 2, etc.) during which the containers are identified by individual production codes for each time interval. (b) Determine the number of sample units in a subgroup as follows: Type of Inspection and Number of Sample Units Normal—25 Tightened—50 Reduced—13 (c) Subgroups are drawn randomly from portions of production throughout the production process and are inspected for defects. The drawing of sampling units may be done in either of two ways: (1) The number of sample units (13, 25 or 50) comprising a subgroup may be drawn at the same time from a randomly chosen point in the production of each portion, or (2) sample units may be drawn individually, but in a random manner, throughout the production of each portion. At least 6 subgroups must be obtained during each basic inspection period regardless of the system used to designate portions of production. (d) A shift to on-line sampling plans from stationary lot sampling plans (or vice versa) during a basic inspection period is not permitted.