It is not possible for the chart to be out-of-control when the R chart is in control.

Question

It is not possible for the  chart to be out-of-control when the R chart is in control.

Quizplus · Accepted Answer

The control of the R chart does not guarantee the control of the mean chart (11ebc114_12f5_6242_8acb_dd43d5d572c3_TB8562_11 chart). The R chart only monitors the variability within subgroups while the mean chart monitors the process mean. It is possible for the mean chart to be out-of-control even if the R chart is in control.

It Is Not Possible for the Chart to Be