Role of Statistics in Achieving Global Consistency of Tolerances

This paper proposes and defends a thesis that global consistency of tolerances is achievable only by consistent use of statistics across specification, production, and inspection. It starts with a global view of variation in a product of an engineering enterprise, embodied in two major axioms: imprecision in manufacturing and uncertainty in measurements. It traces the successful evolution of statistical practices in production and inspection to deal with these variations. Finally, designer specified tolerances are brought into the global picture. Challenges that still lie ahead are summarized at the end.