Turn tables are necessary to measure caster, at least using a bubble level. My bubble level needs the wheels to rotate a total of 40 degrees (20 degrees on each side of center). You can buy turn tables for alignment starting at around $200. Or for around $4 you can use a couple of linoleum floor tile as pictured below. I used my cam degree wheel as a protractor to make the degree lines. A little WD40 between the tiles and epoxy floor allow the tile to rotate with the tires.
The bubble level above measures caster and camber (not at the same time, they are two separate measurements). I also use a Trackace laser to measure toe.
My front end alignment specs todays were:
Caster: Driver side 5.25 degrees positive, Passenger side 5.0 degrees positive
Camber: .5 degrees negative both sides
Toe: Toe in 10 minutes (about 1/16 inches)
Here is a photo of a commercial turntable.
