ISO 7873:1993 PDF

Specifies procedures for the statistical control of processes by using control charts based on calculating the arithmetic average of a sample and using warning limits and action limits. It is assumed that for large lots and for the mass output of piece and batch production, such a measure of quality is a random variable following a normal distribution. However, when averages of four or more items are plotted, this assumption of a normal distribution is not necessary for control purposes.