Began getting left wing skin ready for riveting. Vacuumed out the inside of the wing—many areas will not be accessible once the outboard skin is riveted on. Clecoed the skin to the wing, started with the main spar, worked up the ribs and finally the rear spar. Everything appears to be in alignment. Dabbed a bit of primer on the pitot mast where I had earlier countersunk for the skin dimples.