How do I measure and calculate the degrees to set my saw at to cut a angle.?

I have an odd angled ceiling and have to cut an angle on the top of my crown molding so that I do not have a dust catching shelf.

None of these really help me. I have levels and measuring tapes, and rulers to determine the angle.

tool called a sliding t bevel stick up against wall and duplicate angle on saw
i would use scrap wood first couple trys as may be off little till get used to it
here s a picture of it stanley makes it too this may not not be a stanley here

http://www.vandykes.com/product/02021220

dewalt has a complete tutorial on crown molding here with some more modern tools that may be easier to get a good job done with perhaps this will help you
http://www.altereagle.com/How_to_install...

All you need is a bevel gauge, set one half to the wall, the other to the ceiling, and then use the guage itself to set your saw . . .

Need to determine the angle between the wall and your ceiling, then determine the angle the crown is cut for the portion that fits the wall, probably 45 degrees. Subtact the 45 from the determined angle, and there it is.

Get an adjustable T-Bevel.

You don't need to know the exact angle. After you run the molding through your table saw, the top of the crown will come to a point, like a knife edge. The front of this edge will be up against the ceiling. As long as the angle is acute enough so that the back edge does not hit the ceiling, you should be OK. The top of crown is often slightly angled (beveled) so that it butts up to the ceiling nicely. You just need a more extreme angle.