1980’s version of the hip rafter backing angle formula I used. It was developed from the book
Full Length Roof Framer by A.F.J Riechers
One triangle at a time type of formula
It wasn't very efficient, but at least it was correct for equal pitched roofs.
Roof framing is the Ph.D. of carpentry, it's apparent that Marshall Gross never got his Ph.D. of carpentry.