The AQL viewpoint is based on a traditional defective product definition.
In the classic sense, a product is defective if it falls outside the tolerance limits for a quality characteristic.
Under this view, failure costs are incurred only if the product fails to conform to specifications and an optimal trade-off exists between failure and control costs.
The AQL view permitted and, in fact, encouraged the production of a given number of defective units.
This model prevailed in the quality control world until the late 1970s,
when the AQL model was challenged by the zero-defects model. Essentially,