I believe it is accurate, though I have never taken any of my trucks in after doing it myself to an alignment shop to verify. On my trucks it appears to go 20 degrees from lock to lock. I was doing some reading not to long ago about it and the impression I got was that as long as you were consistent a few degrees more or less really wasn't going to matter. The important things to me are camber and toe in, those are the tire eaters if not correct. As long as the wheel self centers and I'm not having to fight to go into a curve I"m happy and using the gauge allows me to experiment a bit too. All I can say for certain is that I've got 3 daily drivers that I have use this on for the last several years and they all drive great and I've had zero tire issues.

 

Exactly LB. On my 55 I think I was going 1.5 turns of the steering wheel each way to measure it. Just so it's approximately equal on each side it's good. If you don't have power steering and you add too much it's tough to park and things like that. I have a cheap plastic 2' level I cut down to the wheel size to measure the camber. May have to break down and get a tool like yours if I'm going to do different vehicles.

 

Just measure the camber with the wheel turned left, then turn them right. Maybe I don't have nearly the caster I thought if it's only 10° each way? IDK but it's a huge improvement over factory 1955 specs.