XmR Median R Chart Formulas

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The XmR Median R chart uses the Median(R) to reduce the bias in individuals charts.

Using the median helps eliminate bias when there is a "sustained shift in the mean".
Montgomery pg 259.

Here are the formulas used to calculate both the Moving Range and Median chart in the QI Macros.

Compare XmR Individual Moving Range chart and XmR Median R charts to see differences in control limits.

Process: Calculate, plot, and evaluate the range chart first. If it is "out of control," so is the process. If the range chart looks okay, then calculate, plot, and evaluate the X chart.

Other control chart formulas

The XmR Median R chart is just one of the tools included in the QI Macros for Excel SPC Software for Excel.

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