The Process Capability Indices (SPCHART command)

CP. Capability of the process.

CPU. The distance between the process mean and the upper specification limit scaled by capability sigma.

CPL. The distance between the process mean and the lower specification limit scaled by capability sigma.

K. The deviation of the process mean from the midpoint of the specification limits. This measurement is computed independently of the estimated capability sigma.

CPK. Capability of the process related to both dispersion and centeredness. It is the minimum of CpU and CpL. If only one specification limit is provided, we compute and report a unilateral CpK instead of taking the minimum.

CR. The reciprocal of CP.

CPM. An index relating capability sigma and the difference between the process mean and the target value. A target value must be specified on the TARGET subcommand by the user.

CZU. The number of capability sigmas between the process mean and the upper specification limit.

CZL . The number of capability sigmas between the process mean and the lower specification limit.

CZMIN . The minimum number of capability sigmas between the process mean and the specification limits.

CZMAX. The maximum number of capability sigmas between the process mean and the specification limits.

CZOUT. The estimated percentage outside the specification limits. The standard normal approximation is based on CZ _U and CZ _L.

CZLOUT. The estimated percentage outside the lower specification limit. The standard normal approximation is based on CZ _L.

CZUOUT. The estimated percentage outside the upper specification limit. The standard normal approximation is based on CZ _U.

• For each of the keywords (other than CPK), both the LSL subcommand and the USL subcommand must be specified. Otherwise, the keyword(s) are ignored, and a syntax warning is issued. For CPK, at least one of the LSL and USL subcommands must be specified.
• If the TARGET subcommand is not specified, the keyword CPM is ignored, and a syntax warning is issued.