You can take the rotors off and turn them on a lathe which makes them true to the machine and works well but you can also have the rotors turned or machined while they are still installed on the car. This way the rotor is spinning on the hub and trues up the rotor to your vehicle vs. a static machine. A lot of places have on car lathes now which make this easier and more effective. I started doing this on the 80's and 100's since getting the rotor off meant taking the whole hub apart. Am quite happy the 200 rotor replacements are so much easier and wont take hours to so when the time comes.