Control Charts

The image below shows the control limits as they appear on a process control chart. In this case, the example is a mean graph from a mean and range chart.

You can see that 3 lines have been drawn on the chart:

• In the middle (drawn in blue) is the mean, labelled .
• At 3 sigma above the mean is the upper control limit (drawn in red and labelled UCL)
• At 3 sigma below the mean is the lower control limit (drawn in black and labelled LCL)