A quality engineer at an automotive parts plant monitors the variation in the lengths of camshafts. Three machines manufacture camshafts for three shifts each day. The engineer measures five camshafts from each machine during each shift.
The quality engineer creates a R chart to monitor the variation in each machine.
Minitab creates three R charts, one chart for each machine. None of the points are outside the control limits and the points display a random pattern for all 3 machines. Thus, the process variation is in control, and the engineer can examine the process center on the Xbar charts.