A word of caution regarding the use of incidence meters: Check them for plumb. I have a Robart that is about a half degree off. Example: If I check a wing with the meter window facing the left wingtip, and then recheck the same wing in the same place with the window facing the right wingtip, I get a different reading by about a degree or so. (It isn't the vee's; I get the same error checking the top of my building board.) Until I get around to fixing it, I just make sure the window faces the same side of the plane for all the checks.