No need to set zero before use Three V-grooves for shafts (shafts dia. 19.3~115.9mm) With longitudinal vial Code Size (LxL) Sensitivity 4906-150 150x150mm 0.02mm/m(=0.001°) 4906-200 200x200mm 0.02mm/m(=0.001°) 4906-300 300x300mm 0.02mm/m(=0.001°) Check the PDF