Here's the nightmare: You arrive at work to find your best customer has just returned $10,000 worth of precision ceramic parts. They are all neatly boxed and sitting on the inspection room floor with a nasty note saying that they are all out of tolerance. You stand to lose one of your best contracts, not to mention your job, unless you get to the bottom of the problem right away.

So you immediately go to your tool crib and remove your precision digital micrometer from its padded box where it lay with its anvils neatly closed.

First, you check the calibration sticker. The micrometer has a six-month calibration schedule and was calibrated five months ago. No problem there. You check the absolute zero setting on the micrometer. It reads 0.00000". Exactly where you set it when you put a fresh battery in last month. So the micrometer should be OK. The micrometer and the parts have been at the same temperature for several hours, so you should be OK there, too. It's time to check the parts. You remeasure every one of them. They're in spec. All of them.

The customer must be wrong.