Process Capability 1. Use visual inspection to determine whether the process mean is centered between the specification limits. 2. Calculate the process capability index. a. Use ???? ? @ if the process mean is centered between the specification limits. ???? ? @ = ABCDCBC EFG b. Use ???? ? @H if the process mean is not centered between the specification limits. ???? ? @H =min I????????????????G 3????G , ????G???????????? 3????G O USL = Upper specification limit LSL = Lower specification limit ???? = Process mean, which is the centerline between the UCL and LCL. This can be calculated by adding the UCL and LCL, then dividing by 2. ????Q = Process standard deviation, which can be calculated from the control limits, as follows. Calculate the process standard error as the difference between either of the control limits and the process mean, divided by 3. Then, calculate the process standard deviation by multiplying the process standard error by ????. 3. Higher values of ???? ? @ and ???? ? @H indicate a more capable process. Experts recommend a process capability index of at least 1.33 for a two-sided specification. For a one-sided specification that consists of an upper limit only (for example, concentration) or a lower limit only (for example, for strength), the process is considered capable if the process capability index > 1.25