Despite the difficulties of the link, I think it is referring to the Rockwell hardness scale.
The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.1 There are different scales, denoted by a single letter, that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale
As far as the effect of the hardness.
First the harder metal is the longer it will generally hold a sharp edge. So less sharpening involved. Also the hard a metal becomes the more brittle it becomes. This means that the edge could more easily chip or the entire scraper could snap/break.
So as far as actual use, you might be able to use it to do more on harder woods with less sharpening, but you have to be more careful about chipping/breaking it. These are fairly thin pieces of metal so the temper probably needs to be in a relatively small range to keep an edge and to be flexible. better tempering techniques will allow it to be harder toward the edge while leaving plenty of spring in the rest of the tool.