Coin Measurement Discrepancies

I am like BRAND NEW at this so pardon me if I'm in the wrong domain. I will be quick. I have a 1973 coin from Finland, a 5 Pennia denomination. I was checking the diameter and the thickness and comparing my measurements against the data listed for the coin in the website's database. We (the website's database and myself) have been very close all day. I was pretty proud I was doing so well. Until this coin!

I consistently get a measurement of 17.6 mm in diameter with a width of 1.3mm.

The website's database search yielded 18.5 mm diameter and a width of 1.36mm, which I can live with.

A couple of caveats here. My calipers are not the most expensive things in town, but zero is zero and I HAVE been consistently close all day with other coins. The preponderance of the evidence seems to suggest they are adequate for the task. Secondly, I'm "winging" it here. I don't know if there are acceptable methods of measuring the coins that I am not, as yet, privy to. Lastly, I am dog tired and am fully capable of making and repeating mistakes! As it turns out, of course, this is my last coin of the day. I have no idea where these coins came from and who dropped them on my doorstep (hundreds from 78 countries!).

Maybe, just maybe, the whole thing may be a typo (do we have them any more in this hyper modern world?). Maybe 17.5mm was intended to be input; who knows?

I'm done. I don't know if I could find my way back to HERE, so I will give you my email address.
mlm6005@gmx.com

Thank you for your time, something I cannot give back to you!

Mike Martyn

welcome to Numista!!!
Pictures would help