【Accurate Measurement】: Digital PD ruler has clear optical path, precise optical structure, simple operation, and fast and accurate measurement. More accurate than vernier PD ruler. 【Large Display】: The 2 white lines appear very clear against the dark pupils, and the pupil distance is displayed on the LCD screen. The pupillary distance meter has a larger screen and can also be used for the left and right eyes of a single eye. 【Power-off Memory Function】: Digital Pupillary Scale automatically turns off when it is placed on the table and turns on when it is in use to save energy. With a memory function, you don't have to worry about data loss. 【Operation】: It is recommended to have a second person help when testing. Place the PD meter on your nose as close to your eyes as possible. Then find the center of your pupil, the white line should line up with the center. The number displayed on the LCD screen is your interpupillary distance (unit: mm). 【Application】: The digital PD ruler is used to measure the distance between 2 pupils. This is a simple PD ruler that can help you when you want to buy glasses online or at an optical store. If you have very high accuracy requirements, this is not recommended.