suitable for all kinds of inspection work, precision measuring datum plane, cast iron platform; used for machine tool mechanical inspection measuring datum; check dimensional accuracy or shape and position deviation of parts, and make tight marking, it is also an indispensable basic tool in mechanical manufacturing. SURFACE QUALITY INSPECTION OF CAST IRON PLATFORM: inspection by hair color. The level 0 level 1 tablet has no less than 25 points in a 25 mm square area on each side, no less than 20 points on level 2, and no less than 12 points on level 3.