Edgehopper, you are right, but the Rockwell hardness measures only surface hardness. Usually this is enough, but there are exceptions, notably 'hard facing' alloys, such as tungsten carbide (WC), and the cobalt alloys, which are the same hardness all the way through.
Rating these alloys on the Rc scale gives a misleadingly low estimate of how long they will last. For more reading, check out this web site: http://www.ccsi-inc.com/html-tech5a.htm it gives you the details of Rockwell testing and different scales therof.
