The posts above are correct, but to bring a little more technicality to this discussion an R'C' value refers to the Rockwell Hardness value of a certain metal. There are three scales on the Rockwell Hardness scale : A, B, and C. The scales progress from softer to harder A is softer than B which is softer than C. Softer metals are usually measured on the A and B scales but heat treated steel being so hard has to be measured on the C scale. The three scales overlap and that's where the Rockwell measuring system can be quite misleading. The A scale overlaps the B scale and the B overlaps the C. So a high RA (read: Rockwell A value) can mean the same hardness as a low RB and a high RB can mean the same as a low RC. Some people who don't like this tend to prefer the Brinell Hardness scale which is significantly more simple to use. The Brinell hardness (BH) scale is a metric (I think) measurment, so if you see some Euro-made blade advertised with a BH value, it's most likely to mean the blade's hardness. Sorry for being so technical, but maybe it will be useful to someone...