Bacchus gave you the short answer and that's fine. Photograde is an important element of the US numismatic hobby. It goes back about 35 years and is now in the 19th edition. Here is a picture and a brief description: http://www.telesphere.com/books/grading.html Here is a longer review: http://www.heritagecoins.com/features/numisarticles.php?id=213 Ron Guth's website has a couple of out-takes from the book, so you can see for yourself: http://www.coinfacts.com/grading_guide/photograde.htm
