Six Sigma is a method for improving quality by removing defects and their causes in business process activities. The method concentrates on those outputs which are important to customers and translates these customer needs into measurable requirements, the so called CTQs (Critical To Quality). An indicator for the CTQs is identified and a robust measurement system is established to obtain clean and precise data relating to the process. Once this is in place, one can compare actual process behaviour to the customer-derived specification and describe this in a statistical distribution (using mean, standard deviation [σ] or other indicators, dependent on the type of distribution).