| | Interpreting an X-bar/R Chart |
 | | The control limits on the X-bar chart are derived from the average range, so if the Range chart is out of control, then the control limits on the X-bar chart are meaningless. |
 | | Never consider the points on the X-bar chart relative to specifications, since the observations from the process vary much more than the subgroup averages. |
 | | Also on the range chart, there should be more than five distinct values plotted, and no one value should appear more than 25% of the time. |
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