Ever used magnets in a project, and had to fiddle around with it until it worked? Then you should have used a magnetic viewing film, so you could see the problem directly.
In this short video, Will from Tested.com shows us what a caliper is and how it is used. A caliper is much more accurate than most other measuring devices, and as Will says in this clip, cheap enough these days for anyone to afford their own. If you wonder what the sharp pegs on the top side of the caliper is for, it’s for measuring inside holes and other voids.