Bill Smith came up with an efficient method (six sigma) to enhance a process. A process is a set of independent instructions, procedures, and stages. They ingest resources and transform them into products. A process capability measures the potential of a process. That is its ability to produce a product within set limits. Cp and Cpk are such process capability indices.
Bill smith introduced six sigma. Soon it became widely accepted. It is a statistical tool that enhances a given process. Cp and Cpk are process capability indices. There is a condition while calculating Cp and Cpk, that is it should be a stable process. We must analyze Cp and Cpk simultaneously. The reason is Cp ensures the capability of the process whereas Cpk analyzes the performance of the process. Cp judges the variation only. Cpk analyzes both the variation and location of the process.