The DTI method is the most accurate, but can take a bit of time. One fairly quick method is to clamp a bull center in the spindle and adjust the table until the center seats evenly in the RT center hole. This is accurate to a couple of thousands. Another method is to have a plug in the RT hole with a bored hole in the center. Chuck a piece of drill rod that matches the hole and center the table so that the rod can enter that hole.