The aim of a capability analysis is to evaluate the ability of
a process to produce products within the specification limits,
which are defined by the lower specification limit (LSL) and
the upper specification limit (USL). The capability analysis
reveals whether the process produces conforming items, i.e.,
the quality characteristics of the products are within the specification
limits. Corrective actions are required otherwise. For
example, a corrective action can be to expand the specification
limits. In addition, an action to improve the quality of the process
can be also applied. The most common indicator used to
measure the capability analysis of a production process is the
process capability index (Cp), which is defined as the ratio of
the width of the specification limits to the width of the natural
tolerance limits of the process, i.e.,