Statistical Process Control (= SPC) is a continuous accompanying monitoring of manufacturing processes by capturing all relevant to the product quality metrics. The SPC provides the basic data to identify weaknesses and thus the requirement for continuous improvement of their production processes. It may have both quantitative and qualitative characteristics of a product or a process to be monitored.
Data collection and evaluation is done using control charts as a graphical tool, a process over a longer period of time continuously monitored.
In quality control charts warning limits (UWG, OWG) and control limits (LEL, UEL) are defined, above which indicates an irregularity or an error. If you exceed the warning limits means that the process still lies within its tolerances, but a readjustment or intervention is required. Control charts providing an early warning system to prevent errors and committee. Already at the first sign of a mistake can be taken in the process and not only when exceeding the tolerance limits.