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. It s useful for framing and composition for fine art, crafts and photography. It comes with an 8-page instruction booklet.