Statistical process control (SPC) is a method of quality control which employsstatistical methods to monitor and control a process. … Key tools used in SPCinclude run charts, control charts, a focus on continuous improvement, and the design of experiments.

The control chart is a graph used to study how a process changes over time. Data are plotted in time order. A control chartalways has a central line for the average, an upper line for the upper control limit and a lower line for the lower control limit.