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DJN
This may be a silly question, but here goes. Does the data in a control chart have to be normally distributed for the CP and CPk figures to be valid? The process is stable i.e. in statistical control.
Are you using tolerance based control limits or process based ?
Bill Ryan said:
When I use a Control Chart (X-bar & R) with a "natural" limit of zero (True Position, Flatness, Profile, Concentricity, etc.), what "rule" is being violated? I ask because the "underlying data" is NOT normally distributed (typically skewed right), yet the charts sure seem to work!!!!
Bill