For X sensitivity, I have tried 100, 150, 255. And it seems like the first direction I move it in I can get all the way to the edge of the screen. For example, I move to the right and the trackball doesn't move to the edge of the screen no matter how many times I spin to the right, then I spin to left and the trackball doesn't go all the back to center, nor will any further. If I start by moving to left first, the same thing happens, I can never move all the way from the left to the right in centipede or milipede.