Rockwell scale Rockwell 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. 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 (see below). When testing metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of
Carbonate hardness [milli[equivalent]s] per litre (meq/L) or ppm. Carbonate hardness expressed in ppm does not necessarily equal carbonate alkalinity expressed in ppm. formula_1 whereas formula_2 However, for water with a pH below 8.5, the CO will be less than 1% of the HCO so carbonate alkalinity will equal carbonate hardness to within an error of less than 1%. In a solution where only CO affects the pH, carbonate hardness can be used to calculate the concentration of dissolved CO in the solution with the formula CO = 3 × KH × 10, where KH is degrees of carbonate hardness and CO is