DIN 877 - classes 1a / 1b / 2. 1 = DIN 877 class 1a with very high sensitivity longitudinal vial 0.02 mm/m. 2 = DIN 877 class 1b with high sensitivity longitudinal vial 0.1 mm/m. 4 = DIN 877 class 2 with normally sensitive longitudinal vial 0.4 mm/m. Sturdy housing of high quality special casting hammer finish. Vee base with ground contact surfaces in the angle (requirement for marking out, aligning, etc). All measuring faces are exactly parallel to the axis of the vial. One longitudinal and one transverse vial each of acrylic glass. With insulated handles on the housing and protective glass over the vials. For aligning surfaces, shafts, machines etc.