Rockwell test blocks are calibrated and rated in accordance with ASTM E18 and ISO 6508, using NIST Rockwell HRC standard reference materials. All other Rockwell scales are traceable to Wilson Hardness levels through laboratory standardizing test machines. All Wilson Hardness laboratory machines are directly verified according to application ASTM parameters using devices that are traceable to NIST either directly or through a approved laboratory. Please specify the Rockwell Hardness Scale and hardness range.