Massive caster variance Side to side

FWIW...I have the bubble gauge as shown above but instead of Longacre Racing on it, mine says Joe's Racing Products. Same gauge! I used several heavy thick plastic garbage bags folded over a few times as my turning plates. (They worked well as you could turn my manual steer avatar car with virtually no effort.)

Per the ibstructions, I attached the gauge to the spindle, zero'd it out with it at a 20 degree steering angle, then turn to 20 degrees in the opposite direction (total of 40 degrees) and get your reading. I tried it several times just to insure repeatability without making any adjustments. I found it highly repeatable so I was excited to get to set my alignment with my new SPC UCA's I got from Bergman's. Each time I made an appropriate adjustment, it showed up on the reading (meaning the reading showed what I had adjusted). I set the caster to +3.5 degrees on both sides and suddenly I had a car previously unable to be taken down the track reliably (it would go into this left/right porpoising mode unable to be controlled...scary!) to one that leaves dead straight and stays dead straight! So I have to believe that what I set using the gauge was pretty accurate. It sure worked for me!

Let me add though that I am NOT an alignment guru. Just sharing my experience I had with my avatar. I used this same setup to set the alignment on my show pony 71 Demon as well. It seems to have worked out fine there as well although that car was much more of a challenge given it's stock front suspension parts.