[rchowe]

I built a computer vision device that used the top-down area of a penny as a calibration standard. Coins are useful, easy-to-get items that have relatively tight manufacturing tolerances.

[cassepipe]

What about wear ? Were they only new coins ?

[wongarsu]

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

[rchowe]

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.

[Retric]

I’ve never seen significant ware on a coin in circulation.

Have you?

[qup]

Also a penny is .750 exactly. None of the other US coins have a "useful" diameter.

[dotancohen]

The US nickel is so close to 5 grams that I've seen them used as weights in a laboratory.