As a general rule of thumb, trackballs will have one roller parallel with, and closest to, the face of the monitor for the vertical axis and another perpendicular for the horizontal axis, on the left. The wires on most units exit somewhere near the lower right corner when viewed from above. It's possible to swap axes and directions by manipulating the wiring, but that's not usually the best approach for most installations, as it is pretty much accepted that the aforementioned orientation is the most versatile, based on the physical interactions of the ball and the rollers.