The approach developed herein is to find an 'implementable' common denominator notion for the different Quality categories - a notion from which all the definitions can be considered corollaries. Consider three from the previous list:

• "Quality is the degree of excellence at an acceptable price and the control of variability at an acceptable cost." (Broh, 1982)
• "...to improve process and product design through the identification of controllable factors and their settings." (Taguchi)
• "Quality is inversely proportional to Variability" (Montgomery)

These imply that Quality arises from variables that can be defined and then measured (using devices) or assessed (perhaps using devices, but certainly agreement). Most, if not all, of these definitions can actually be translated into concepts of 'variability from some predetermined gauge'. Simply put, Quality can be composed of a set of variables, which can be measured or assessed and compared to predetermined optimum goals. This formalization of quality can be expressed as shown below where the larger the value for Quality, the smaller the variability in the product - or the closer to the optimum goal.

Note that variability would never go to zero in a real world. Here Variability is the set of all variable qualities of a product, which are measurable or assessable such as reliability, features, color, weight, performance criteria, regulated requirements (legal, patent, regulatory agency, industry standards), environmental, human factors... etc. (Here, 'qualities' comes from Webster's definition "That which belongs to something and makes or helps to make it what it is; characteristic element; attribute.") For any product (or service or process, for that matter) Variability is defined as measurable or assessable changes in all of a product's attributes, which are determined to be relevant to a Quality product.