I don't know what a cross slide, compound, or leadscrew is, I'm just curious about the trig and geometry of a wedge as it relates to the ring. I am not seeking any precision, I am just trying to understand the SP calculations for SEL and board length, not to question the software or use more precision in my creating rings."If you are trying to get to 'surgical' precision you should think of a different hobby."
Exactly. Have you noticed there is no cross slide, compound, or leadscrew on a wood lathe? There's just no need for that level of precision. Even if you turned a piece to that level, it's going to change and move next spring anyway.