Don't get too upset that Rusty can't eyeball things he only has one.(a polecat or something like that got the other one when he was young) Besides that he's a curmudgeon.The 5° measurement is worst cast. I have no cherry to break and you're coming across pretty defensive. I'm just pointing out that you can eyeball it and have results that are 99.6% as accurate as a $$$ tool.
So yeah if you can't eyeball 5° (or better) then get a tool that will do it for you.