You return your attention to her work and flip to her third sheet. This one, it seems, is mostly written for your benefit. It details some quirks about the spell Twilight needs to make this whole contraption work. The calculations in the first sheet, it turns out, were Twilight playing with different values to take burdens off the spell itself. The more power provided by mundane means, the less work the spell needs to do, so the longer it would last and the easier it would be to cast. The same is true with mechanical linkages; the spell could apparently make a leg without a knee just by positioning two sticks, but giving one a groove for the other to rest in made it easier, and a fully-formed hinge easier still.