[jimmux]

I was going to say it might depend whether the angle is measured along the middle of a face or along an edge, but with a face angle of 51.5 degrees I calculate an edge angle of 41.6 degrees.

That's assuming I still know how to trig, and it's entirely possible I don't.

[stan_rogers]

Middle of the face, and probably more like 51.8° originally. That corresponds to base faces measured in turns of a measuring wheel and a height of the same number of wheel diameters, which would be an incredibly sensible way of laying it out (letting the tools do the calculation for you).