The Atomic Aquatic Gauge Reader Lenses for the Atomic Aquatic Sub Frame Mask (see SKU's: ATMMSF or ATMMSM) allow you to see things clear underwater with positive Bi-Focal Diopters. The Diopters are available from +1.5 to +2.5 in +0.5 Diopter increments both left and right lens. Are tempered safety glass, easy to install and will make seeing underwater better to increase your diving safety. Lenses are sold in pairs.