Homework Assignment: Errors

Not every oddball coin is an error.
Most oddballs are intentionally damaged by people, or unintentionally by the environment, machines out in the real world, or contact with contaminants.
You have to do a little homework on your own.

This is your assignment for today: Check out http://www.error-ref.com/

Read the whole site. It explains a great many error types, how they are created, and pictures to go with them.