If using Minitab to determine Process Capability, un-select “Within subgroup analysis” in “Capability Analysis (Normal Distributions) – Options,” and enter the value 1 for “Subgroup size.” Minitab will calculate “Overall” Standard Deviation, equivalent to (ref. 3.5), and will return “Ppk,” which is equivalent to the definition of Cpk given above (ref. Appendix B1). The use of Minitab is not required; other statistics software products may be used.