An XmR chart (aka Shewhart’s Control Chart aka ImR chart) is a chart where the control limits are calculated from the moving average range.

## Use XmR Control Charts When:

• When you have continuous data.
• When you have subgroups of size = 1.
• You use the ImR (XmR) chart only when logistical reasons prevent you from having larger subgroups or when there is no reasonable basis for rational subgroups.
• Particularly useful when you are only making one observations per time period.

## XmR R Control Chart Definitions

Range: Based off of the consecutive differences in measures. First, find the average of your measurements. Then calculate the absolute

## How to Create & Use XmR Control Charts

• List all of your measurements
• Calculate the moving range by absolute difference between each measure by subtracting one from the other in sequential order.
• For example, if you have measures of 4, 6, 3, and 5, you will then get the following differences:
• (4-6) = 2
• 6-3 = 3
• (3-5) = 2
• Calculate the mean of the samples.
• In our example the mean is 4 + 6+ 3 + 5 = 18.   18/4 = 4.5
• Calculate the mean of the individual moving ranges. This will act as the control limit – plot this horizontally on the graph.
• 2 + 3+ 2 = 7. 7/3 = 2.333
• Calculate the Upper & Lower Control Limits.
• UCL = Sample mean + 3* MR mean / d2
• LCL = Sample mean – 3* MR mean / d2
• d comes from a chart – you can find this in most reference books like this one.
• The 3 refers to 3 standard deviations.
• UCL in our example would =4.5 +  (3 * 2.333 / d2)
• LCL in our example would =4.5 –  (3 * 2.333 / d2)
• Plot upper control limits (ucl) and lower control limits (lcl)

## Important notes on XmR Control Charts

• Remember to NEVER put specifications on any kind of control chart.
• Use an X Bar S chart when the sample size is > 10.
• Use an X Bar R chart when the sample size is <10.
• Use an XmR chart when the sample size s 1.

## IMR Video Prasad V. Dhawle says:

First of all, thanks for the important & useful information provided here by you, with detailed explanations.
I have a query that, here in “X-mR Chart” information page, you mentioned “X Bar R” chart word throughout the page. I think, there may be some typographical mistake, i.e. ‘X Bar R’ instead of ‘X-mR’.
Please confirm and clarify my doubts, and do the required changes.

Thanking you in anticipation.

Thanks & Regards, Ted Hessing says: