OMG, @PCO you just showed me something I never paid any attention to. Forget the math example! Wouldn’t you know the computer (LightBurn) already does it. You were just measuring the wrong side of the angle.
Solution =
Draw box snapped on upper and lower segments then use those nodes to find angle! WOW. It was right down there this whole time.
Look at the bottom of the screen when I draw the two line segments, you will find the same 11 degree angle:
