Methods and formulas for potential capability measures in Normal Capability Analysis

Cp

Notation

TermDescription
USLUpper specification limit
LSLLower specification limit
TolerMultiplier of the sigma tolerance (Minitab uses 6 as the default value)
Within-subgroup standard deviation

CPL

Notation

TermDescription
Process mean (estimated from the sample data or a historical value)
LSLLower specification limit
TolerMultiplier of the sigma tolerance (Minitab uses 6 as the default value)
Within-subgroup standard deviation

CPU

Notation

TermDescription
USLUpper specification limit
Process mean (estimated from the sample data or a historical value)
TolerMultiplier of the sigma tolerance (Minitab uses 6 as the default value)
Within-subgroup standard deviation

Cpk

CCpk

Minitab calculates CCpk based on known values of LSL, USL, and T.

Known value CCpk
USL only
LSL only
LSL and USL

where:

Notation

TermDescription
Estimator for the population mean
USLUpper specification limit
LSLLower specification limit
Within-subgroup standard deviation
Average of the observations
TolerMultiplier of the sigma tolerance (Minitab uses 6 as the default value)
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