Ever since coin clipping got out of hand in the 1700s most coins feature milled edges or edge inscriptions. They make the edges more resistant to wear and make any wear easy to spot.
Of course there's a limit to the precision you can get from coins, but considering the scale of their production and the account of handling they see they are surprisingly good
Our area measurement application did not require that tight a tolerance (we were estimating yield on broken material). If I needed that tight a tolerance, I could have gotten proof coins from the mint, or potentially switched to using a real calibration standard like a gauge block.
I have often, though I suspect not enough to make a significant difference to someone who is already OK with the slight variance between un-worn coins.
Depends on what your tolerances are. If you only need to be within a mm a coin is going to beat that by an order of magnitude.
We use a pack of cigarettes as a gauge for one of the jobs we do. Quick, (not so) cheap, and readily available. May have to standardize on a vape though in the near future.
