1. Simple to use, very convenient, and widely used 2. Designed by the principle of optical refraction, it is an optical instrument with high precision and easy to carry 3. Eyepieces, eyepieces are comfortable and easy to view, the field of vision is clearer and can protect the prism from damage 4. The calibration screw, drop distilled water on the prism, turn the zero adjustment screw, the dividing line is adjusted to 0% of the scale 5. The cover plate protects the prism from other factors, thus affecting the stability of the measurement