P.D Rule digital
Gulden’s Digital PD Ruler is a simple and inexpensive way to measure both monocular and binocular distances between eyes. This is necessary for accurate fitting of various ophthalmic lenses, especially multi-focals. It works by simply aligning the vertical stripes over the center of each papillary reflex. R button measures right eye, L button measures left eye. No button measures distance from between the eyes. Very accurate and responsive digital display Automatic shutoff when place on level surface.