This table shows capability and performance indices.

Capability indices. These measures assess the ability of the process to perform to specification. Each statistic measures a different aspect of the process.

CP is the ratio of the difference between the specification limits to the observed process variation. CP values greater than or equal to 1 indicate capable processes. Values less than 1 indicate that the process is too variable. The CP value of 0.762 indicates that the variability in the pH of the samples exceeds specification. CpL and CpU help you to determine whether or not the process variability is symmetric. If their values, as in this case, are close to CP, then the process variability is relatively symmetric. K is a measure of the ability of the process mean to approximate the center of the specification limits. Smaller values of K, combined with larger values of CP, indicate that the process stays within the specification. CpM measures the process capability, adjusted for its ability to stay on target. If CpM is close to CP, as in this case, then the process has stayed on target. Performance indices. These measures are similar to the capability indices, but tend to be more conservative because they are based on the overall process variability rather than the sample variability. If the performance indices are considerably smaller than the capability indices, there may be nonrandom variation in your process. Here, the performance indices do not appear to be much smaller than the capability indices.