ISO 9000 & AUDITS WORLD CONFERENCE ABSTRACT
Don't Be Misled by Specification Limits
A specification limit is the universally accepted ‘litmus test’ that we all agree to abide by. Specification limits seem quite simple to use and apply. After all, if the product or service being delivered is measured and found to be in-between the Upper and Lower specification, it is accepted as good. It is so clear, so black and white, how could anything be gray about applying this concept? In fact, if this was the only rule, it would be hard to argue that something is “In” or “Out” of spec. In tennis, the Hawk Eye line-calling system is used to determine if the ball was inside the line, hit the line (but still considered in), or outside the line. In the quality improvement world we live in, anything measured outside the specification limits is unacceptable. Given this operational definition of acceptance, there should be no ambiguity. Unfortunately, there are problems in this naive world of acceptability. Customers do not simply want a product produced or service delivered anywhere between the specification spread. They want two things: 1) the measured value to be at the desired target and 2) minimal variation.