The process data section of the capability analysis graph consists of the following:

·    Upper and lower specification limits (USL and LSL) - the limits you specified.

·    Target - the target value you specified.

·    Mean - the mean of all measurements, which is where the process is centered.

·    Sample N - the total number of observations in your data.

·    Within standard deviation - a measure of the variation within subgroups.

·    Overall standard deviation - a measure of the variation of all the measurements.

A substantial difference between the overall and within capability indices may indicate that the process is out of control, or the sources of variation are not estimated by the within-subgroup component of variation. For the piston data, the within and overall capability indices are very close to each other.

For the piston data:

·    Upper and lower specification limits (USL and LSL) - the LSL is 73.95 and the USL is 74.05.

·    Target - the target is 74.

·    Mean - The mean is 74. Note that the mean is very close to the target of 74.0, which implies that the process is centered on target.

·    Sample N - 125 pistons were measured.

·    Within standard deviation - The within standard deviation is 0.0100509.

·    Overall standard deviation - The overall standard deviation is 0.0101989.

The within and overall capability indices are very close to each other.