Grumble grumble grumble grumble....

So just when I thought I was stripping, I noticed a form that was pretty clearly not vertical. I'd made my L brackets (below is an older picture to show the brackets) out of pine blocks with a dado and plywood, and used deck screws to screw everything together. Bill pointed out that I need to use a clearance hole to make sure everything screws up tight or there can be gaps, which was the problem here.

After going back and fixing the obvious offender, including releasing it from the strips so it would adjust, I knew that screwing everything down super-tight will not give me perfectly vertical forms, because my strongback is not perfectly flat. I have a framing square that I can use to check vertical-ness of forms by measuring with the top string (can't use bottom string or strongback because the other stations are in the way). Several of the forms are slightly off vertical.

I know how to measure it (framing square) but not correct it. Do people use shims for this? Is there a way to know when I'm close enough? The square at the shop is pretty huge (~2') and tiny deviation shows up clearly.