Machinist School - Precision Measuring vs Schizophrenia

The picture above is supposed to be animated. If you are not seeing motion, click on the + at the center of the picture.
If you watch the rotating dot, you see pink dots and a rotating dot. But if you stare at the + the rotating dot turns green. Then the pink dots begin to disappear, leaving only the rotating green dot. This is an optical illusion ....
That is why machinists use a variety of measuring instruments ..... too many optical illusions. Of course, many of the tools "looking". By using different measuring tools, we can look at an object from a "different point of view". If we get the same measurement using different tools, our measurement is said to be confirmed; we have confirmed our finding. Or, using actual machinist language, "Yup, it was exactly what I thought it was in the first place!"
If somebody else gets the same measurement we did, our results are validated. In the vernacular, validated is, "Yup, what he said!"
Schizophrenia? If you see a green dot that isn't really there, don't worry about it. It is better to be "seeing things" than to be blind.