The Mk. VI was the top of the Combat Master line. The rear sight was adjustable via interchangeable leafs, and the I believe there was some hand-fitting of the lockwork. Not all Mk. VI's were marked "Professional Model", and I don't know if that marking is prevalent or orare among Mk. VI's. Prices run from a low of $500 for a nice, but used example, to over $700 for a minty one with factory accessories.