The Select-A-Scale twelve-inch engineer drafting ruler is a unique and inventive aluminum engineering scale with a rotating calibration rod. It is made from high-quality extruded aluminum with ultra-smooth edges. Fixed scale is 50 parts per inch, and the rotating scales are 10, 20, 40, 10:1, 20:1 and 40:1. This scale is an ultra-convenient and functional drafting tool that allows the user to select multiple scales all in one product. This item is a sleeker and more portable version of the more-traditional triangular drafting scale.