I keep seeing the question on how to do this and this is how I learned so many years ago from RCU when I started flying so I figured I'd post a pic so you could see what all the people are talking about, Works really well on high wing, Low wing and even biplanes like mine. The only thing that might be tough is finding a good plumbob, I made mine at work but many don't have that opertunity as I do in a machine shop but if you find a good alternative please post so others can use the ideas.

Enjoy
Dauntae