Process Z is the point on a standard normal distribution such that the area to the right of that point is equal to the Average P (the proportion of defective units in your process). The higher the process Z, the better the process performance. Ideally, you want a process Z of 2 or more.
You can use Process Z in Binomial Capability Analysis to estimate the sigma capability for attribute data. Process Z describes the capability of a binary process - a process in which products are judged to be either defective or not defective.
The process Z values is available in the results of your binomial capability analysis.
Suppose the defects are in column C1 and the subgroup sizes are in column C2 of your worksheet. The process is in statistical control and rational subgroups were collected to reflect the inherent variation of the process.