Control Limits

The graph at the top of the chart has been suitably scaled, and the following lines drawn on it:

• the Upper Control Limit (UCL_x)
• the Lower Control Limit (LCL_x)
• the grand mean ()

Similarly, the scale, together with the lines for UCL_R, LCL_R and the mean of the R values () are shown on the R graph.

The position of each of these lines has been calculated from previously recorded data, in order to:

• establish the criteria for statistical control for this process
• prepare the Chart for plotting

The chart footings, below the recording boxes, are used for calculating control limits. Because those calculations are beyond the scope of this course, you can simply ignore that section.