|UCL = Upper Control Limit|
|LCL = Lower Control Limit|
|= 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 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.
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