The Starrett ProSite protractor takes error-prone calculations out of the process of miter cuts. Simply set your saw to the angle that you read. Upside down or backwards, the reading is always correct. This easy-to-use tool has 2 scales. The red scale and arrow show the angle for a miter joint, while the black arrows and scale provide the angle to fit a single workpiece to an angle. The ProSite protractor saves time and reduces waste. It's ideal for carpenters, plumbers, and all building trades that require the measuring and transferring of angles. It's also invaluable for home use.