Pupillometers for Measuring Pupillary Distance (PD), PD Ruler, Essential Tool for Single PD or Dual PD Measurement > High quality PVC material, flexible, lightweight, high transparent, easy to use. Your ideal measuring handy tool when buy glasses online. > Classic straight edge design for using with both eyes, Nose bridge design helps hold the PD ruler centered and stationary, accuracy guaranteed. > Distance in millimeters of PD measuring range: 23mm~42mm each side, complete PD is between 46mm to 84mm. PD Ruler