The skins are creased slightly to prevent "oil canning" while flying. Basically, the creases stiffen the large areas of unsupported skins between the fuselage ribs. During this process, small notches are cut in the skins at the ends of the creases. Though it isnt mentioned in the manual, I decided it would be a good idea to file those away to avoid spots where possibly cracks might form later.
The instructions are predictably vague in this entire chapter, and with all the fitting I feel like is necessary before riveting, I think I will run short of clecoes.
Note the small notch in the skins that need to be removed
