No need to set zero before use V-groove on bottom for shafts (shafts dia. 19.3~115.9mm) With longitudinal vial Code Size (L) Sensitivity 4905-160 160mm 0.02mm/m(=0.001°) 4905-200 200mm 0.02mm/m(=0.001°) 4905-300 300mm 0.02mm/m(=0.001°) 4905-500 500mm 0.02mm/m(=0.001°) Check the PDF