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The below table describes the most commonly used control charts.


Type of ChartDescriptionFormula
P-ChartClassification Data
c-ChartCount data 

u-ChartCount Data


X-ChartVariable Data


S-ChartVariable Data


The most common Western Electric rules to identify special causes:

  • any points outside the control limits
  • A run of 8 or more points all above or below the center line
  • A trend of 6 or more points up or down
  • Two out of 3 points near a control limit
  • Fifteen points close to the center line


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Last modified: 3/3/2009