Don't buy this piece of shit or any of these trackballs unless you have a medical condition that prevents you from moving mice, or you have totally unconventional computer setups.
I bought pic related because I use the keyboard a lot, and removing the extra space for the mouse had the potential to make my experience more comfortable, but it didn't help at all, and the trackball doesn't even come close to matching a mouse in terms of precision for normal use. In the end, I solved the problem just by adjusting the relative position of the monitors, keyboard, and mouse on my desk.