Wayne, you're just like me. When I'm cutting wood on the table saw, I'm trying to get each cut to the nearest 32nd of an inch. Thanks for the great response! I'm convinced. 15" is actually perfect as that is the top of the mouth of the F20 horn. At that height; should I use 3 or 5 degrees? I'm leaning toward 5 just because it seems like a rounder number. But, maybe I'll do 4 degrees?