In this photo I'm using a ratcheting strap tie-down to pull the left wall square. The tie is attached to the top of the left wall and then to the bottom of the back wall. Tightening the tie-down effectively pulls the top of the wall toward the back of the house, while, of course, the bottom stays still. With the wall square I can then apply the sheathing which will take on the job of holding the wall perfectly square.