Stewart Warner Electric wheel Balancer

My wife's grandfather used to do safety inspections back when Idaho used to require them. I have been put in charge of determining a price for the shop equipment.

Found this wheel balancer, looks like it maybe worked with the wheel on the car? Or maybe we are missing another component. Anybody have any knowledge on it?

 

I bought one over the weekend at a swap meet for $10 . It’s not a shiny as yours .

 

There is a motorized roller that spins the the tire while it is on the vehicle. I’m missing that piece of equipment.