Two tools in one! This is a lightweight, portable, durable, clear ruler AND a goniometer, which is a tool that enables you to precisely measure angles–such as the angle of the sun, the angle of branches of a tree, the angle of a flower stem to the plant, etc. I have this tool in my daily nature journal bag, and I notice that when I have a handy way to measure length and angles, I include more lengths and angles in my journal. Measures in inches and centimeters. Measures angles 0 to 180 degrees, and when fully open, it can measure a total length of 36cm (14in).