To increase product quality and predict the unqualified products, effective control methods must be selected. Considering the disadvantages of process capability indices
Cp and
Cpk that are hard to help to find the reason of quality problems and direct quality improvement, three new indices
Cps,
Cpc, and
Cpc available in real time are introduced to control the scatters and errors. Finally the feasibility of these indices is proved by an application.