For critical processes, where safety or high costs are involved, tests of normality, such as Chi-Square, are used to determine whether data are normally distributed. Therefore, one can draw a bell-shaped curve around the histogram. Shift of 1 s in the process mean. The bell-shaped curve is characterized by two parameters, mean and standard deviation. In other words, it is the ability of the process to produce product around the target or process mean value.
Process capability is a measure of variation in the process.
An example of process capability data is shown in Figure 1. Since we know probabilities associated with the normal distribution, the probability of producing product within specified tolerance can be estimated. Cp and Cpk can be used to predict a process' ability to produce within specification limits or the specified tolerance. Cp, the process capability index, is a measure of the inherent capability of a process to produce product within the specified tolerance and is determined using the following formula. The borderline acceptable value of Cp is 1, which is sensitive to producing defects.