This is a quick square and it is used for framing. I find it very handy around the house just to do quick little jobs. It's got a lip on here so that you can put it up on a piece of wood and instantly you can have a perpendicular or 45 angle off that. So just put it up against here, draw a line and you are all set. It comes from a frame you square because it does have angles on here and you can actually use it to cut root rafters at the right angles but you want to be using that for regular abound the house. It also has a regular scale on it, 07 inches this one; some come big, some are 12 inches deep but this is a very nice handy size one and say you are just putting up a small wall in your basement or in your play room , you can use this to easily mark lines so you know where your studs go. For instance say you had a mark there, you can put a mark and then you would measure off an inch and half, put another mark, put an x there you know that is where one stud goes. Then you measure over typically 16 on center, do the same thing. So when you place your stud here, you will know exactly where to put it and you will know if the stud is perpendicular to this. If it is out of canter, you can just get it right in and line it up with the line you've made using your quick square. So I find it very handy device to have around the house if you have any kind of small framing jobs.