Variance, or variation in the way we present a product is one of our greatest hurdles in quality management. Just consider. If you have a favorite pizza shop, and one time you get a bad one, are you finished doing business with them? The "bad" one may have been ok, just not consistent with their usual product. Replacing your pizza shop may be simple enough, but what if you need transmission parts on a massive scale? You need to be able to work with suppliers (and vice versa) to be sure that variance is limited. What are the tools that you consider to be critical to quality management?