Which way does the back panel go on a bookcase?

Question

Accepted Answer

Flush with the bottom and both sides, with its finished face showing, nailed onto a frame you have squared by measuring both diagonals.
In our demo bookcase the back is two panels of 3 mm hardboard, 80 × 96 cm each. They go on in step 9, with the bookcase lying face down:
Measure both diagonals of the frame, corner to corner. Equal diagonals mean the frame is square.
Place the lower panel flush with the bottom edge and both sides.
Nail it every 15 cm along both sides and along the fixed shelf.
Repeat with the upper panel.
The 24 nails are 1.4 × 25 mm, tapped in with the hammer. Measure before the first nail, not after: the back panel locks the frame in whatever shape you nail, so a frame nailed out of square stays out of square.
Two earlier steps decide whether the back can sit flat. In step 1 you find the side panels' raw edges, which face the back, where the back panel covers them. In step 7 both sides must sit flush at the front before you turn the cam locks: a 2 mm overhang there becomes a wobbly back panel later.
On a bookcase that stands against a wall, the side that shows is the inside, behind the shelves, so the rough face of the hardboard goes to the wall. If your own manual's drawing shows it the other way, follow the manual.