What is sigma in SPC and how to calculate sigma value in CP, CPK.

Question

Accepted Answer

Sigma is a statistical measure of process variation in SPC. CP and CPK are used to calculate sigma value.

Sigma is a measure of how much a process deviates from its target value.
It is calculated using the standard deviation of the process data.
CP and CPK are used to calculate sigma value in SPC.
CP measures the capability of a process to meet the customer's specifications.
CPK measures the capability of a process to meet the customer's specifications, taking into account the process mean and standard deviation.
A higher sigma value indicates a more capable process with less variation.
A sigma value of 6 indicates that the process is capable of producing only 3.4 defects per million opportunities.

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