Sunwin 48mm-77mm Optical Digital Pupillary Distance Meter Pupillary Distance Measuring Tool with LCD Display Optical Pd PDs 1.ACCURATE COMPARED TO OTHER PUPILOMETER READING-Cornea reflection light coincidence method is used. This operates by aligning luminous points on the pupils with the measuring line. 2.TURN OFF AUTOMATICALLY- Automatic power shut-off in one minute after operation is completed. Store device flat side down, it will turn off automatically. 3.DISPLAYED IN 3 MEASUREMENTS - Right, Right/Left, Left.By emitting point on the pupil alignment and measurement of light measurements can be carried out in two ways by monocular and binocular Data display range: eyes IPD 44-83mm 4.EASY TO USE AND EXCELLENT PRICE -It is extremely easy to use and it's also very comfortable and not that heavy. It alos has multiple PD settings. 5.Our Guarantee:If you are not satisfied in any way with our product, please feel free to contact us first we will do our best to resovle all problem you have .