Vintage Alignment Systems

I have those same ones but with the degree pointer: 25-140-P Quality Passenger Mild Steel Pointer Plate - Black

Mine do not slip.

I'd have a tough time paying $600 for set of them. They are pretty basic tools, but lot of metal $ to them. I see some Chinese ones on Amazon. Easy for me to say, I lucked out on a set for $75.
Cost more to ship it than you paid for yours. (Yes, you did luck out.) Well, I went ahead and ordered them anyway. The ones on Amazon weren't cheap either. Nor is taking a bunch of cars to an alignment shop. Can I learn a new skill at my advanced age? Guess we'll see. :)