I measured, cut and built the first of the rear spars...however what I measured was from the 'outside' of the wing rib where the spar passes through instead of the internal section. My choice was to source locally grown hoop pine and machine new caps and verticals or disassemble the spar and start again. I pulled my thicknesser out and proceeded to gradually machine the plywood off. Once removed I jigsawed the verticals off right at the top and bottom and then recut each to the correct ie. shorter size. The caps were sanded back to their original and the building process began yet again.