Squared up the frame with:
- Big square, 18x24 inch
- Skin. It is perfectly square

Then clampled in:
- Square
- Skin
- Hinge
- Rear end of ribs

Checked alignment of primary datum at:
-Rear end of skin with rear spar
- Hinge with end of rear spar
- 75 inches of rear end of spar with skin and hinge
- Spar drill lines with pilot holes in skin

Once squareness and alignment was checked, pilot drilled:
- Rear spar and hinge using skin pilot holes
- Ribs