Today, the capability study is a universally recognized method to formalize process control. The classical Cp and Cpk indexes are not the best indexes to express quality in production. The Cpm index is more representative of this quality. This article proposes a generalization of the Cpm index specifically designed for unilateral distribution. This new index issuing from Taguchi's loss function offers significant advantages in comparison to Cpk. We discuss different examples of Cpm calculations and interpretations.