Mark; The metal lathes usually have a way to adjust the horizontal alignment of the tail stock. The lathe is setup at the factory for the head and tail stock to be accurately aligned vertically. To check the alignment, put points in both the head stock and tail stock and bring them together. Trap a thin piece of steel (feeler gauge) between them. The feeler gauge will twist in the direction of mis-alignment.
On wood lathes the tolerance is much greater and there usually isn't any adjustment. I have seen people add adjusters to lathes.