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Cp is one of several indices used to measures Process Capability. Cp is used to predict potential process performance:
Where:
| USL, LSL |
Upper and Lower Specification Limits |
| σ R |
The process standard deviation. It must be estimated by the range method. See Process Performance |
When Cp was originally conceived a spread of 6 standard deviations was 'state of the art' quality. The '6' in the denominator was used so that a Cp value of 1 or greater indicated a 'capable' process. Since then standards have increased and now a minimum Cp value of 1.67 is usually required.
Cpk is a closely associated process capability index.
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