1, the left and right borders of glasses should be kept relatively flat;

2. The left and right leaves of the spectacle frame should be symmetrical;

3. The external opening angles of the left and right temples of the glasses are 80 ~ 95, which are symmetrical;

4. When placed in Zhang Kaiping or prone, both temples are kept flat and the frame cannot be twisted;

5. The inclination angle deviation of the left and right legs is not more than 2.5;