Description
Dr. Deming, the person most often associated with statistical process control, once observed that if you measure something once, you know what size it is, but if you measure it again, you no longer know its size. What Dr. Deming was referring to is the fact that no measurement is exact and thus measurements do not exactly repeat. In order words, the millimeter that you measure is not the same as the millimeter that I measure and is not even the same as the millimeter you measure tomorrow.
