Process variability
Statistical process control — Using control cards

The use of simple statistical techniques to manage a manufacturing process enables :

• to prevent the effects of maladjustments instead of suffering them and to sort production a posteriori;

• avoid 100% control (control of all units produced);

• rationalize sampling plans (number and frequency of checks) rather than choosing them "by experience" (often by inspiration).

These statistical techniques use the method of evaluation by checking a sample limited to a few units (n) to estimate the mean value and dispersion of all the units produced. For the chosen characteristic X, the average $\overline{x}$...