Cost-effective; Use high reliability; Use general components (blade bearing etc.); With background light, readable (even in dark environment); Digital display unit and battery external, effectively cope with cooling fluid and clastic; Digital display and manual mode can match use; A digital display unit can deal with all size boring cutter (0.3 to 2400 mm); Has the magnet adsorption function, easy to operate, can adsorption in any conveniently places. Use standard cell (9 v).