The hardware store owner said a level needs regular calibration: take a reading, spin it a hundred and eighty degrees, take another, and half the gap between them is your error.
I turned the one at home around, and the bubble settled in a different spot each way, off by about one mark.
Between the day it was bought and that afternoon, it had checked a bookshelf, two shelf boards, and a refrigerator, and had called every one of them straight.
All three are still where they were, so which gets measured again, them, or the tool that just got caught leaning?
Best used for: For tool maintenance, measurement error, or any time the one who kept saying it's fine had never been checked.
Variations (2)
- Short version: Turn it around and the tool admits it's a mark off.
- Extended: Nothing it approved has moved; the approval has.