In the Statistical process Control Reference Manual published by AIAG, capability falls under 2 categories; long-term and short-term. On page 59, Long-term capability is denoted as Cpk and uses an estimated process standard deviation while short-term capability is denoted as Ppk using the calculated standard deviation. It has been argued and published by many statistical program companies that Ppk is long-term and Cpk is short-term. the reasoning for this confusion relies on the definition of what long-term and short term is and how it relates to the standard deviation. What is the definition of Cpk and Ppk and why do most software companies publish process capability contrary to the statements in the AIAG manuals?