Why does a combination lock re-lock when you close it?

Question

After you put in all of the numbers in a combination lock, all the little doodads inside it are lined up so that it can open. So, if you close it, and the dial is still on the correct last number, then why does it relock itself?

Answer 1

Because the cylinder turns when the shaft closes. There is a little grove that causes it to turn to the next spot inside the lock.