First hang the device on the glasses frame, and align the center point with the center point of the nose bridge of the glasses frame. There are knobs on the left and right, and the knobs can be moved to adjust the pupil height measuring piece, so that the upper edge of the measuring piece is aligned with the pupil center, and the pupil height value is read at the lower edge of the frame.
Clean with dry cloth, and keep clean, do not heavy