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X Bar Chart Calculations

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X Bar Chart Calculations

Plotted statistic

Subgroup Average

Center Line

Grand Average

UCL , LCL (Upper and Lower Control Limit)

knowctr00000079.gif

knowctr00000080.gif

where x-double bar is the Grand Average and knowctr00090004.gifx is Process Sigma, which is calculated using the Subgroup Range or Subgroup Sigma statistic.

Notes: Some authors prefer to write this as:

knowctr00000081.gif

knowctr00000082.gif

where R-bar is the Average Range , or

knowctr00000083.gif

knowctr00000084.gif

where S-bar is the Average Sigma .

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