1. Gradient method measurement of AC/A2. Measure the pupil distance and select a trial frame that is consistent with the pupil distance;3. The refractive error of the subject's eyes is completely corrected;4. Insert +100-degree spherical lenses in front of both eyes at the same time;5. Insert a Maddox rod lens in front of the right eye to keep the Maddox rod grid stripes horizontal;6. Place the proximal Torrington plate 40cm in front of the eyes, turn on the power, and keep the light source and the line of sight horizontal;7. Ask the subject about the positional relationship between the light source and the vertical line he sees, and record it;8. Remove the +100-degree spherical lens, and then insert a -100-degree spherical lens in front of both eyes at the same time;9. Ask the subject about the positional relationship between the light source and the vertical line he sees, and record it;10. Subtract the first recorded value from the second recorded value, and then divide it by 2, which is the AC/A value.Power Supply: 2 x AA batteries(Not included batteries)Colour:WhiteMaterial:ABSPackage Contents:1 * Squint Vision Detection Tool1 * StandOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.