I recently bought a place with a large and nice new shop. The floor here is much more level than my old place, so I decided I could probably just put the scales on the floor with shims and dispense with leveling frames. I'll need to re-do my hillbilly platen, this time with just chunks of 4x4 and plywood.
Years ago I bought a precision Chinese level .0005/10" and while it is accurate, just getting started with leveling can be a fiddly royal PITA, so I thought I could build a simple water level on the cheap to get me in the ballpark and boy does this work better than anything I've done in the past.
The level is built from 4 qty half-liter graduated cylinders from amazon, and a bunch of nylon 1/8 inch tubing nipples from the local do-it center. About $25 bucks in all. A little green food coloring in a liter of water and I was in business in less than an hour.
Took just two iterations to get to within .025. You set the cylinders up on the pads and read the heights on the graduations. The one with the lowest reading is the highest pad, and serves as the reference. In the case of the cylinders I bought, the graduations are about .1" apart. I should probably spend a few minutes under higher magnification to be a bit more precise. You can easily read to .050, and with a few drops of water wetter in the fluid at this diameter you don't have to consider the meniscus.
So you can directly read the height differences from the reference at each scale, and I picked some pieces of flat stock as shims to see where I'd get. put the shims under the cylinders, let it stabilize for a few minutes, and took another reading. I needed another .050 here and there, shimmed those, and I believe I am now within .025 across the set. Now, if I want to go to the precision level and a beam I won't be chasing my ass for an hour.
I have some relatively ancient Reb-co scales that are 3.5". Besides the shims, I've also thought of just drilling the bottom plates for #10 flat head screws, because once I set the heights I'll never have to touch them again. I have no real platen and I don't re-scale at the track, If I need to do so I'll look for someone that has a set or a trackside shop and pay to rent them.