used for measuring thickness and corrosion of pressure vessels, chemical equipment, boilers, oil storage tanks, etc. in industries of petroleum, shipbuilding, and machine manufacturing. tm-8812, tm-8811, can measure any hard materials, including steel, cast iron, aluminum, red copper, brass, zinc, quartz glass, polyethylene pvc, gary cast iron, nodular cast iron and other materials. tm-8810,can measure only 11 types of materials, including steel, cast-iron, aluminum, red copper, brass, zinc, quartz glass, polyethylene, pvc, gray cast iron, nodular cast ironb ultrasonic thickness gauge tm|8811f used the exclusive micro-computer lsi circuit and crystal time base to offer high accuracy measurement & fast measuring time.