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XmR Control Charts (also known as ImR Control Charts) are Individual and Moving Range Charts. They are used when the subgroup size is one. This may be when logistic reasons prevent larger subgroups, but is more commonly when there is no basis for rational subgroups.
The chart is based on the moving range between consecutive samples:
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Upper Control Limit
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Lower Control Limit
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Moving Range Chart
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Upper Control Limit
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Lower Control Limit
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D4 and d2 are taken from standard tables, based on a subgroup size of 2:
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