Larry, Great questions. If you figure anything out, let me know. *GRIN*
For leveling a 24 foot long ledger, I don't know of any way to do that super accurately and accessible. You could use a four foot audible level and just keep moving it around, probably not the most accurate or easiest way to do it. If you have eyes available, a water level would be a pretty good idea. As far as finding the centers of the joists for attaching the plywood. First, put your plywood in place, top side down on the joists. Then place strips of tape on the plywood, from underneath, next to each joist. You could put the tape on both sides of each of the joists so you don't have to remember left right stuff. Then flip your plywood over, making sure you flip front to back and not left to right. If your joists are reasonably straight the tape will now bracket the joists below the plywood. For plumbing up your support poles, you can use an audible level and just move it around the pole until you get it sounding vertical on two adjacent sides. See, easy peasy, nothing to it. *GRIN* -- Blue skies. Dan Rossi Carnegie Mellon University. E-Mail: [EMAIL PROTECTED] Tel: (412) 268-9081
