A tip to avoid having to draw all those lines for rib stitch spacing; use a thin, flexible strip (about 1" wide) of fiberglass, like what you trimmed off the wingtips, to mark your stitch spacing. Always line up this strip with the trailing edge; much easier. Also very handy for tweaking the spacing to avoid underlying structure; just move it from rib to rib and check structure interference, slightly readjust your marks until one spacing plan works on all ribs. You will need a separate strip for top and bottom.