In laying out forms, its often easier to cut out a piece of stiff cardboard (like 11 1/2 square) and use that as your measuring spacer rather than a ruler. (assuming your plywood is 1/2" thick) A large square piece will also help in getting the stations square. Plans that are generated on a design program make the stations a position that is thin like a piece of paper. So when we build, we can use whatever thickness of plywood we want but have to compensate for the thickness of the wood. Most designs are 12" on center.