Control Chart

A control chart is a statistical process control tool that plots a process measurement over time against a center line and calculated upper and lower control limits, so a manufacturing or business process can be monitored to distinguish ordinary, expected variation from a genuine, correctable shift in the process itself. The American physicist and engineer Walter A. Shewhart developed the control chart in 1924 while working at Bell Telephone Laboratories, seeking a way to reduce the variability of manufactured telephone equipment by separating common-cause variation, inherent to a stable process, from special-cause variation that signals something has actually gone wrong. Shewhart's chart became the founding tool of modern statistical quality control and was later popularized industry-wide by his colleague W. Edwards Deming.