The graph below illustrates the results of an actual process optimization effort. The red distribution represents one of the “worst” process performance levels and the green represents the “best.” Not surprisingly, the settings that produced the green distribution were chosen for this process. This selection resulted in a process capability of 8.8, and a process mean 26½σ from the upper specification limit. The d²σ process was not pursued directly; it resulted from the optimization effort and was the least expensive way to run the process.