I wish to drill four evenly-spaced holes in a ball. How do I form my construction lines so that my marks are accurate? Obviously, if I could circumscribe a tetrahedron inside (or outside) the ball its vertices (or face-centres) would mark my holes. But I can't do that. I need to scribe my marks on the ball. I suppose my first start would be to know the angle between two vertices (perhaps organic chemists might know the bonding angles of a carbon atom?) Is that the dihedral angle (which Wiki sez for a tetrahedron is 70.5degres)? Does that mean any two holes would be 70.5 degrees apart? Cuz I think I can do that.