If you ever have or ever intend to install crown moulding, you will appreciate this tool. It gives you the actual angle of the corner, inside or outside corner. And, it gives you the miter angle. Just set your mitersaw to the angle and make your cut. No more open miters, no more trying to make that second cut. http://www.amazon.com/gp/product/B0000DCBLW/ref=pd_ts_c_th_1_3/104-1533875-7909541?%5Fencoding=UTF8&v=glance&n=228013 Recently, I used this to mark my top angle on fascia at the peak of a gable. I have found countless other excuses to get this tool out, you will too. The tool works by swinging the halves of the tool to the positon where the final product will be, right against the walls, the tool is tight enough to keep this setting until you can get a reading. Very handy, Tom in KY, angle master. Not compensated nor affiliated with the Starrett company or Amazon.