Checking Caster

[Skip Fix]

So I got a DIY setup to do front end stuff.




So doing the 15 degree caster sweep 15 degrees one way then turn the wheel the opposite 15 past center and read. Well the brackets on the tire are then no longer perpendicular to the ground. So read it where it sits, change it back to perpendicular and read it?

Rear tires are chocked no no roll that way, double garbage bag "turn plates" but I really do not think front tire is rolling since the back is chocked down.