If you do any amount of trim work you need this tool. It's more than an expensive bevel gauge. Yes it measures angles ,inside and out, but it does a whole lot more. We have specific angles and bevels we use for cutting crown mold. What if the angle of your corner  is not 90 degrees? By following the instructions and pushing a button a few times , this baby will do the math for you. Giving both bevel and miter angles for any wall angle. What if the crown you bought has a different back angle than what you are accustomed to ? This will help you find that too . It really saves valuable time. The only thing I would like to see is a smaller version to get into tighter places. Oh well I do have a bevel gauge and a protractor.