ViewCatcher is an innovative plastic device that slides open to provide a viewing window to help frame compositions. The square window is 1 15/16" wide when fully opened, and has indicators for standard proportions used for framing purposes, such as 8" x 10", 12" x 14", etc. Made of durable, mid-gray ABS plastic, it has a convenient thumb grip for opening the viewing window. A small round opening in the center of the sliding window allows you to determine the value of the colors you are viewing. Itís useful for framing and composition for fine art, crafts and photography. It comes with an 8 page instruction booklet.