The 900-375 tests both Regular Rockwell Hardness and Superficial Rockwell Hardness in one unit, "Twin Tester", with state of the art design and dynamic precision only found at Phase II. The Phase II Twin Regular/Superficial Rockwell unit is ruggedly engineered to obtain highly sensitive and accurate readings. Conforming to ASTM E-18 standards, this unit will offer unmatched repeatability in all Rockwell hardness scales. A perfect performer suited for any environment including heat treatment facilities, tool rooms, knife makers, workshops, laboratories and inspection labs. Free lifetime technical support is included with all Phase II units. So test away with confidence and a level of accuracy you will only find at Phase II.