Similar to Cpk, Ppk is a capability index that indicates whether a process is capable of meeting two-sided specification limits. However, Ppk uses actual standard deviation to calculate the process variation, whereas Cpk uses an estimated standard deviation. The target value is taken into account with Ppk, so the system does not have be center on the target value to be useful. A Ppk greater than 1 indicates that the process can meet the specification.