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Why is the your chart before the x chart?


Asked by Fernanda McLean on Nov 30, 2021 FAQ



Thus, the R chart is examined before the {\displaystyle {\bar {x}}} chart is examined to determine if the sample mean is also in statistical control. If on the other hand, the sample variability is not in statistical control, then the entire process is judged to be not in statistical control regardless of what the
Thereof,
Interpreting an X-bar / R Chart. Always look at the Range chart first. 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. On the Range chart, look for out of control points and Run test rule violations.
Furthermore, Unfortunately, you may need to fit a distribution to the data to effectively use the Individual-X chart to determine if the process is in control. Because of this limitation, you may consider using other control charts, such as the X-bar Chart or Moving Average chart to first define process control.
Besides,
The control limits on the Individual-X chart are derived from the average moving range, so if the Moving Range chart is out of control, then the control limits on the Individual-X chart are meaningless.
Likewise,
A typical pattern is shown in Figure 1. Such a pattern on the X chart may result from systematic environmental changes such as temperature, operator fatigue, regular rotation of operators and/or machine, or fluctuation in voltage or pressure or some other variable in the production equipment.