XmR Individuals Chart Formulas

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The XmR (Individuals and Moving Range) chart can help you evaluate a process when there is only one measurement and they are farther apart: monthly postage expense and so on.

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

Conforms with ANSI/ASQC B1, B2, B3 1996

QI Macros Versions as of April, 2009 and later:

The XmR Charts employ the Nelson Rule for Moving Range:
Any moving range (R_i) greater then 3.5*Rbar should be removed from the average moving range calculation.

In example below, point 20 (46.50) is greater than 3.5*11.14 (original Rbar), so it will be removed from Rbar Calculation which changes Rbar to 9.73 and UCL/LCL for both the X and R charts.

Source: Control Charts for Individual Measurements, Lloyd S. Nelson, Journal of Quality Technology, Vol. 14, No. 34, July 1982.

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

• Create a XmR Individuals chart in Excel using the QI Macros
• XmR Individuals chart video
• XmR Individuals chart template in Excel
• Other control chart formulas

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

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