A PROFESSIONAL'S CHOICE - Alvin has been the professional's choice for drafting tools and drawing supplies for over half a century. Since 1950, we have brought quality and value to our customers. Our tools help bridge the gap between ideas and innovations We are known for our wide selection of high quality tools at a fair price. VERSATILE USAGE - Ideal for calculating length and distance in classrooms and/or real world applications. You can see through the optically clear acrylic body of the triangle; clear acrylic, adjustable angle, triangle, 0.12 inches thick, 12 inches. THUMBSCREW LOCK MECHANISM - Use the thumbscrews to keep and adjust the angle you want locked securely in place at your desired rise, slope or angle. INCLUDES RISE AND SLOPE GRADUATIONS - Hot stamped graduations that will help you with your rise, slope and degrees. And with the inking edge its a lot easier to make sure your measurement is precise. COMES WITH DETAILED INSTRUCTIONS - To help you and guide you on how to use the triangle properly.