When I assembled the wing, laying down the spar and fitting the ribs to the bottom spar all of the ribs tips were flat on the building board. After inserting the upper spar some of the rib tips lifted off the building board. I had to cut out one of the ribs and sand the notch in the rib slightly to get it to sit correctly. Had I proceeded to attach the TE without first re-seating the rib I would have inadvertently built in a warp.