The hardest part of all was attaching the top plywood to the subfloor. I marked everything before the top plywood was in place. You have to be extremely accurate and consistent with you marking. when top plywood in place you can not see tubes
. I used floor screws instead of nails. My floor feels like made of concrete. You can not even tell this is wood structure. Even floor in living-room which is 500 sqf and floor is suspended (no walls below for support) feels the same solid.