As I glued the ribs in I made sure they were straight up and down. The yellow tool there is handy it is square on the bottom, and you can use it for degrees. I used it to bevel the ailerons on my four star. Sorry I didn't post more pics as I was going on step by step, I just got in a bit of a hurry. The first rib is on a bit of an angle and the template has a bit of a curve on it. so I used the tool with the degrees to recheck. I put it on the drawing in the book as a reference.