Installing crown molding and baseboards is a delicate matter requiring precise measurements of the angles. You can use various tricks and techniques to try to get the angle for a cut but most of these techniques are just estimating the closest angle. When you estimate the angle you never get a perfect fit and look for your crown molding or baseboards. To ensure a perfect fit you must know how to properly measure the angles to know the exact angle to cut the piece of wood.
Measure the inside angle of the wall. Loosen the screw on the degree finder and place it on the corner of the wall. Open one of the legs of the degree finder until it is touching one of the two walls and open the other leg so it touches the opposite wall. Tighten the screw on the degree finder to keep the degree measurement locked.
Read the degree indicated by the degree finder. The red indicator arrow will be pointing at a degree measurement. This is the size of the inside corner angle. To use this angle measurement to cut the piece of wood, you must divide the actual measurement by two. For example, if you have an inside angle of 90 degrees then you divide this number by two and you get 45 degrees. The 45-degree measurement is the angle the miter saw must be set to to cut the wood at the correct angle.
Measure the outside angle of the wall with the degree finder. Loosen the screw on the degree finder and place it on the outside edge of the wall. Push each end of the degree finders legs so it is resting on the wall. Tighten the screw on the degree finder to mark the degree. Read the degree on the finder as indicated by the red arrow and proceed to divide the degree by two to set it up on the miter saw.