Alvin 18" center finding ruler features zero-point in center of rule with increments to left and right. Allows quick location of center between any two points. Especially useful in picture matting, photo layout, woodworking, locating button holes and pleats in pattern making. Faster than using dividers and eliminates guesswork. Bottom edge is a standard rule. Calibrated two edges, one side; reverse side plain. Top edge graduated in 1/32"; bottom edge 1/16". Durable, light-weight aluminum construction. 12" RULER SHOWN IN PHOTO.