The variety attribution tutorial on NGC's website describes different classes of die varieties and how to distinguish them.
An illustrated guide to attributing varieties of United States coins has been added to the VarietyPlus webpage at www.NGCcoin.com. This is one of several useful articles found there which provide a greater understanding of what varieties are and how to distinguish them properly. The VarietyPlus webpage may be found under the “Research” header on the NGC homepage.
Prepared originally for the “Light from many Lamps” program at the American Numismatic Association’s Summer Seminar, this tutorial describes the different classes of die varieties and how to distinguish them from would-be varieties. It is illustrated with NGC-certified coins covering many types and series and is presented in an entertaining and easy to understand manner.
To link directly to this tutorial click here