Pp index

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Pp index Process Performance Index. The ratio of the tolerance (allowable range of values for a specification) to the variation of values in a sample. Variation is shown as standard deviation.

Pp = 1 variation equals the tolerance.

Pp < 1 variation is more than the tolerance (bad).

Pp > 1 variation is less than the tolerance (good).

For a normal distribution, the formula looks like this: File:Pp six sigma formula.png