Yeah, a cheap Sears inclinometer is what I use. I need fairly recent prescription reading glasses to read the scale, too. The first time I did my own alignment over twenty years ago, I didn't need reading glasses.
It can take the better part of a day to get a car set up taking repeated measurements to verify consistency, but once I have the alignment where I want it stays put.
For those inclined to do this you get caster readings by taking camber readings with the wheels at extreme right and left lock and then subtracting one from the other. On a car with close to zero caster getting the sign right can be tricky, but since Mercs have a lot of positive caster it's easier to keep track.
The slab in my garage is my "surface plate", and it seems flat enough to get consistant and true readings.