%Off-Target is a diagnostic measure that represents the percent of the specification range the mean falls from target. This measure is calculated by the following formula.
- USL is the Upper Specification Limit,
- LSL is the Lower Specification Limit,
- T is the Target, and
- is the sample mean from all combined data.
As the process average departs from target, Ppm is reduced. The figure below graphically displays the relationship between Ppm and %Off-Target. The resulting Ppm is shown for four levels of Pp (at infinity, 3, 2, 1.5, 1) as the offset from target varies. The highest line represents a process with a standard deviation of zero (Pp at infinity). If a process is running with a mean 10% off target, the largest Ppm that may be achieved is 1.67. At 30% off target, the largest Ppm that may be achieved is 0.56.