Purpose

Control charts are used to monitor a process to see whether it is in statistical control. The UCL and LCL - or upper and lower control limits - indicate how much variation is typical for the process. Points that fall outside the limits, or into particular patterns, indicate the presence of a special cause of variation.

How does it do it ?

• Focuses attention on monitoring process variation.
• Serves as a tool for ongoing control of the process.
• Distinguishes special causes from common causes of variation.
• Provides a common language for discussing process improvements.