Control Limits

UCL = Upper Control Limit
LCL = Lower Control Limit
x-bar = average of individual X values

On this graph, we have the same information as shown on the run chart, but instead of showing the specification limits, we have drawn on the process's Control Limits (marked UCL for Upper Control Limit and LCL for Lower Control Limit. The third line, labelled x-bar represents the process's mean (i.e. the average length of the steel beams).

The Control Limits represent the natural limits of the process, i.e. what it will produce when it is working normally.


What type of variation is displayed in this data?

Common Cause
Special Cause

Choose an option and then click the button to check your answer.