SURELY, WE ALL RELY on measurements. They form the inputs for both engineering designs and theories; they allow us to assess whether our designs and theories work. We need the measurement system to be above reproach. When we put it on the witness stand, we want to be sure it tells "the truth, the whole truth, and nothing but the truth" . . .

The Whole Truth. . .We can cross-examine each component in the measurement system to check whether it is a trustworthy witness, by noting certain component characteristics---such as rise time and bandwidth. We thus make sure that the system can handle the process it has been asked to observe.

And Nothing But the Truth. . . A measurement system can tell us more than we want to hear. But with proper care, we can prove---beyond a reasonable doubt---that it responds only in the desired way, and only to what we want to measure.