A review of specification limits and control limits from the perspective of Six Sigma quality processes

While specification limits represent voice of the customer, control limits address voice of the process. Specification limits and control limits are treated as independent entities until modified control limits are proposed which stress the need for control limits to keep satisfying specification requirements as well. High quality processes always attempt to provide products right the first time where specification requirements are checked for controlled processes. This calls for a strong link between control limits and specification limits. A house of quality-like representation can be used to describe such a link. It is preferred to intertwine the features of specification limits with the construction of control limits to achieve right the first time. In this paper, a critical review on specification limits and control limits is made from the perspective of Six Sigma quality and the need for a strong bond between the two is stressed.