The Starrett ProSite protractor is constructed from durable engineered plastic and has a nonstick coated O-ring for smooth and precise operation. This protractor is economically priced, eliminates calculations, reduces errors, and provides greater accuracy for miter cuts. Simply set your saw to the angle shown on the protractor. Upside down or backwards, the reading is always correct. This easy-to-use tool has 2 scales. For a miter cut, the arrow on the handle points to the angle on the inner scale, and for a single cut, the center arrow points to the angle on the outer scale.