Tramming the Tailstock
One method used to center the tailstock with respect to the tailstock is to mount a dial test gauge in the spindle & a dowel pin in the tailstock-mounted drill chuck; another method uses the dead center. The test dial indicator is mounted in a collet. Rotate the spindle front & back while adjusting the tailstock off-set, making half-the-difference changes between them until there are no differences. Use the basic principles of this technique to tram the mill, vise & rotary table, too.
CAUTION: DO NOT TURN THE LATHE ON
Also see tramming the 9x20 lathe.