Question: what is the difference between single pupillary distance and dual pupillary distance?
Answer: Single PD (or binocular PD) is the measurement from pupil to pupil between each eye. Dual PD (or monocular PD) is the measurement from your nose bridge to each eye. Dual PD is believed to be the most accurate since many people may find their nose-to-pupil measurement is not equidistant on both sides.