I have a magnetic base camber gauge that came with a used tool box I purchased at a garage sale. It appeared to be a viable option for use on my Miatas. So, my son and I made a tool that can be placed against an OEM 15″ Miata wheel.
The tool is made from scraps of steel left over from the string jig and a couple of pieces of angle iron that came from Tractor Supply. We welded it together and painted it with silver wheel paint to match the string jig.
I also used a homemade water level to check the level of my garage floor. It was level on three wheel locations and 1/2″ low on one. I can use floor tiles and one piece of 1/2″ plywood to use to level my cars to check the camber.
With the string jig and the camber tool I can do a basic alignment.