Marked a center line on the spar at (10mm) & ribs at (8.5mm). I used 8 web ratchet clamps to bring the skin down to the skeleton. Then, I lined up the center lines through the predrilled holes in the skin, drilled with a #40 bit & clecoed (updrill later). When top section of skin was bent down it came out to be 3mm shorter than the lower section of skin at the trailing edge. I marked & trimmed off the 3mm to make the trailing edge flush. Released the clamps & removed the clecoes deburred all holes & cleaned with lacquer thinner. Primed all mating surfaces with zinc oxide (spray cans).