Process Capability and Performance Variables

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Process Capability Variables

Cp/Cp2

Capability or potential of the process. A ratio of the specification width to the width of the normal distribution. Cp is normally calculated using an estimated standard deviation formula that uses either the mean of subgroup ranges or the mean of subgroup standard deviations with constant table values relative to the subgroup size.

~cp~

Returns Cp calculated on Tol (Tolerance).

~cp2~

Returns Cp calculated on Tol2 (Tolerance 2).

~process,cp~

Capability or potential of the process baseline. The ratio of the specification width to the width of the normal distribution. Cp is normally calculated using an estimated standard deviation formula that uses either the mean of subgroup ranges or the mean of subgroup standard deviations with constant table values relative to the subgroup size.

Cpk/Cpk2

Capability of process index relative to dispersion and centeredness. From the true process center (), Cpk indicates the closest specification limit (in terms of estimated standard deviation units/3).

~cpk~

Returns Cpk calculated on Tol (Tolerance).

~cpk2~

Returns Cpk calculated on Tol2 (Tolerance 2).

~process,cpk~

Capability of the process baseline index relative to dispersion and centeredness. From the true process center (), Cpk indicates the closest specification limit (in terms of estimated standard deviation units/3).

Cr

~cr~

Capability ratio. The reciprocal of Cp.

~process,cr~

Capability ratio using the process baseline. The reciprocal of Cp.

Cpm

~cpm~

Capability of process index influenced by the difference between the sample mean and the nominal target value.

~process,cpm~

Capability of the process baseline index influenced by the difference between the sample mean and the nominal target value.

Process Performance Variables

Pp/Pp2

Process performance index relative to dispersion. A ratio of the specification width to the width of the normal distribution. Pp is calculated using calculated or sample population standard deviation.

~pp~

Returns Pp calculated on Tol (Tolerance).

~pp2~

Returns Pp calculated on Tol2 (Tolerance 2).

~process,pp~

The process baseline performance index relative to dispersion. A ratio of the specification width to the width of the normal distribution. Pp is calculated using calculated or sample population standard deviation.

Ppk/Ppk2

Process performance index relative to dispersion and centeredness. Ppk is calculated using calculated or sample population standard deviation.

~ppk~

Returns Ppk calculated on Tol (Tolerance).

~ppk2~

Returns Ppk calculated on Tol2 (Tolerance 2).

~process,ppk~

The process baseline performance index relative to dispersion and centeredness. Ppk is calculated using calculated or sample population standard deviation.

Pr

~pr~

Process performance ratio. The reciprocal of pp.

Level Analysis Variables

The Sigma level variables are shown as Cpk, but can be used for either Cpk or Ppk level analyses. See here for information about the DataStack Level Analysis.

Sigma Level Numbers

~cpkALevel~

Returns the 6 Sigma level (0-6) for Cpk.

~cpkBLevel~

Returns the 6 Sigma level (2-4) for Cpk.

~cpk2ALevel~

Returns the 6 Sigma level (0-6) for Cpk2.

~cpk2BLevel~

Returns the 6 Sigma level (2-4) for Cpk2.

Sigma Level Values

~cpkALevel,[0-6]~

Returns the 6 Sigma level (0-6) for Cpk.

~cpkAlevel,0~

 - Cpk < 0.33

~cpkAlevel,1~

 - Cpk >= 0.33, < 0.67

~cpkAlevel,2~

 - Cpk >= 0.67, < 1.00

~cpkAlevel,3~

 - Cpk >= 1.00, < 1.33

~cpkAlevel,4~

 - Cpk >= 1.33, < 1.67

~cpkAlevel,5~

 - Cpk >= 1.67, < 2.00

~cpkAlevel,6~

 - Cpk >= 2.00

~cpkBLevel,[2-4]~

Returns the 6 Sigma level (2-4) for Cpk.

~cpkBlevel,2~

 - Cpk >=  < 1.00

~cpkBlevel,3~

 - Cpk >= 1.00, < 1.33

~cpkBlevel,4~

 - Cpk >= 1.33

~cpk2ALevel,[0-6]~

Returns the 6 Sigma level (0-6) for Cpk2.

~cpk2Alevel,0~

 - Cpk < 0.33

~cpk2Alevel,1~

 - Cpk >= 0.33, < 0.67

~cpk2Alevel,2~

 - Cpk >= 0.67, < 1.00

~cpk2Alevel,3~

 - Cpk >= 1.00, < 1.33

~cpk2Alevel,4~

 - Cpk >= 1.33, < 1.67

~cpk2Alevel,5~

 - Cpk >= 1.67, < 2.00

~cpk2Alevel,6~

 - Cpk >= 2.00

~cpk2BLevel,[2-4]~

Returns the 6 Sigma level (2-4) for Cpk2.

~cpk2Blevel,2~

 - Cpk >= < 1.00

~cpk2Blevel,3~

 - Cpk >= 1.00, < 1.33

~cpk2Blevel,4~

 - Cpk >= 1.33