This innovative tool is a 3-1/2" square plastic device that slides open to provide a viewing window to help frame compositions. The square opening is 1-15/16" at its largest point, 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 your are viewing. ItÃ†s useful for framing and composition for fine art, crafts and photography. It comes with an 8-page instruction booklet.