Proof is the highest grade, or the best condition possible. The Mint makes Proof coins differently than reg. coins for circulation. The blanks are polished to a mirror finish, the dies used to stamp the coins are also polished and each coin is struck twice for the best detail. They are then sold to the public at a premium price in singles and Proof sets that are produced in limited quantities. The system of grading ranges from 1 to 70. 4 is good, 8 is very goof, 12 is fine, 20 is very fine, 40 is extra fine, 55 is almost uncirculated, Uncirculated or Mint State coins range from MS60- MS65, and Proof range from PF65- PF70. I hope that helps you understand the basic scale.