A method determining the extent to which the long-term performance of an industrial process complies with engineering requirements or managerial goals. Often it is required that output should lie between upper and lower specification limits (USL; LSL). One measure of the extent to which this is achieved is the potential capability, C_p, given by where σ is the standard deviation of the output distribution. An equivalent statistic is C_r, the capability ratio, which is 1/C_p.