X Median R Chart Formulas

The XMedianR chart works just like the XbarR chart except that it uses the median instead of the average as a measure of central tendency.

Here are the X Median R chart formulas used in QI Macros for both the Range and Median charts.

Range Chart formula

x median r chart formula

 

X Median Chart

x median chart formula

n = number of samples in a subgroup

k = number of subgroups used to determine the average median and range

Conforms with AIAG SPC 2nd Edition

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 Resources

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


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