This is the system that refaces discs on the car.
Having had problems with disc warpage (or if you want to be pedantic, whatever phenomenon causes the damn things to run out and wobble) I have traced the problem to a warped hub on the L front wheel. New discs made only a little difference to the problem when changed 1500miles ago.
This device has now machined the discs to match the hub and for £85 I have 2 perfectly true discs without a trace of judder that has plagued me for the last 25k miles.
FYI, both discs were measured as having a runout of less that 2thou before machining.