The iterations stop when satisfactory results are obtained. Quality is something we all look for in any product or service we get. It is a measure of the extent to which customer expectations and satisfaction are met. It is not static and changes with time. Continuous quality improvement program is a MUST to stay competitive in these days.
Variability is present in machines, materials, methods, people, environment, and measurements.
Need to understand the variability. Statistically designed experiments are used to find the optimum settings that improve the quality. There is no such a thing as good statistics or bad statistics. It is the people who report the statistics manipulate the numbers to their advantage. Statistics properly used will be more productive.