Cp Cpk % out of tolerance

To check if the data set is according the specification.

Cp (Process capability if centered)

Calculates the Cp value of a dataset, and is only calculated if there min and max tolerance are available.

Formula

The process capability when the if the process is centered between the specification limits. With a higher Cp value the data set is better within tolerance.

Cpk (Process capability)

Calculates the Process capability value of a dataset.

Formula

With a higher Cpk value the data set is better within tolerance.

Cpk	sigma level	% out of tolerance	PPM out of tolerance
0.33	1	31.73	317310.508
0.66	2	4.55	45500.264
1.00	3	0.27	2699.796
1.33	4	0.01	63.342
1.66	5	0.0001	0.573
2.00	6	0.0000002	0.002

% out of tolerance

Calculates how much % of the data set is statistical out of tolerance. Below 0.1% the value is displayed in PPM (Parts Per Million).

Formula

calculate the value out of the t distribution.
calculate the value out of the t distribution.

% out of tolerance is

Legend

= Mean
s = STDEV
USL = Upper specification limit
LSL = Lower specification limit
sigma level = http://en.wikipedia.org/wiki/Three_sigma_rule

Example

From dataset in column A the CP is 1.2, Cpk 1.05 and statistical is 871 PPM out of tolerance, this is visible in the rows: Cp, Cpk and % out of tol of the result array. The values will be calculated with the tolerance borders in Max Tol. and Min Tol.

External links

• http://en.wikipedia.org/wiki/Process_capability_index
• http://www.itl.nist.gov/div898/handbook/pmc/section1/pmc16.htm
• http://en.wikipedia.org/wiki/Three_sigma_rule
• http://en.wikipedia.org/wiki/Parts-per_notation