One of the most important tasks of quality control is to make sure products meet their specifications. In the past, quality control inspectors rejected defective parts during a 100% inspection of the product. The development of mass production allowed a single factory to produce thousands of parts a day. A factory would have to hire and pay many skilled workers to inspect each of these parts, which can be expensive and time-consuming.
Simply throwing out parts with defects can also potentially cost the factory a lot of money. This is partially because doing so does nothing to prevent the defect from recurring. To save money, a factory needs to be able to determine if there is a trend in defects and to correct the process before producing defective parts. Statistical Process Control (SPC) is a method that replaces 100% inspection and solves both problems.