Dang, I hate it when that happens. Yeah, I should have remembered the way
the Rockwell hardness test goes. I was relying on my old memory... The
numbers were all generally close though.

They tested two items; hardness and toughness. Hardness is pretty
straightforward using the Rockwell hardness test so they just gave the RC
number for each chisel. Toughness is a little more subjective and this is
where they provided the ranking from 1 to 17. They ran the chisels through
a test then measured the roughness of the edge down to approximately 1
micron (9,500 measurements across 1 inch). From this roughness data they
rated the toughness of the edge.

No mention of the chisel composition.

As I mentioned in another post, this review is now 4 years old and they only
tested 17 chisels out of hundreds (thousands?) available so it all has to be
taken with a grain of salt. I couldn't figure out any hard-and-fast rules
based on brand (e.g. Sears was tougher than many others), country of origin
(e.g. not all Japanese chisels rated high), or cost (e.g. several lower cost
chisels beat out higher cost chisels). Seemed to be something of a crap
shoot to find the "right" chisel.

--
Larry C in Auburn, WA

"Jim Wilson" pointed out Larry's confusion plus
more...