The Barska Aa10313 Monocular (10 x 25) is a pocket size monocular that is ideal for sightseeing, or travelling. The 10 x 25 refers to magnification/power of the monocular. The first number refers to the magnification of an object or how many times closer an object is seen at 1000m distance. The second number refers to the diameter of the objective lens expessed in mm and the larger this number the more light comes in and the brighter the images..