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Xbar & R Control Charts are probably the most widely used type of Variable Control Charts in Statistical Process Control.
They are used as a pair, the Xbar (Mean) chart plots the mean of subgroups that are taken periodically from the process. The R (Range) chart plots the range of the subgroups. See 'Rational Subgroups' for guidance on how to select subgroups.
The control limits are calculated from:
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Upper Control Limit
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Lower Control Limit
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R Charts
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| Upper Control Limit |
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| Lower Control Limit |
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The factors are taken from standard tables.
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