Our inspector uses the most common international standard: Military Standard MIL STD 105E (equivalent to ISO 2859) for inspection.

This standard gives inspection sampling by attributes for a given batch size and acceptance quality level. An inspection plan includes the sample size/s (n), the acceptance number/s (c), and the rejection number/s (r). The single sampling procedure with these parameters is as follows: Draw a random sample of n items from the batch. Count the number of nonconforming items within the sample (or the number of nonconformities, if more than one non-conformity is possible on a single item). If the number of nonconforming items is c or less, accept the entire batch. If it is r or more, then reject it. In most cases r =c+1.

Acceptable Quality Level (AQL)
The inspection level determines the relation between the batch size and sample size. Levels I, II, and III are general inspection levels:

• Level II is designated as normal. 
• Level I requires about half the amount of inspection as level II, and is used when reduced sampling cost are required and a lower level of discrimination (or power) can be tolerated. 
• Level III requires about twice the amount of inspection as level II, and is used when more discrimination (or power) is needed.             

The four special inspection levels S-1,S-2,S-3,S-4 use very small samples, and should be employed when small sample sizes are necessary, and when large sampling risks can be tolerated.The AQL is generally specified by the authority responsible of sampling. Different AQLs may be designated for different types of defects. It is common to use an AQL of 2.5% for major defects, and 4% for minor defects.

Below is a download of how acceptance sampling method is used.

Supplier and Consumer Risks
The supplier risk is the ris that a batch of high quality (according to the AQL) is rejected.
The consumer risk is the risk that a batch of low quality will be accepted.

Assumptions
The sampling table is based on a homogenous lot of products, and is assumed   that the batch is manufactured on one single production location. If the batch consists of products originated from multiple production locations, this will influence the homogenous quality of the sample selected for inspection.

It is important to understand that acceptance sampling cannot imply 100% error free products. Continuous process improvement by the factory is the way to achieve 100% error free products. 

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