I've had 2 surface pro with the same problem. It doesn't matter how much I calibrate it and the methods, there seems to be a zone of the surface (at the center near the bottom, where the taskbar is) that always seems to be inaccurate. I know about the corner problems, but I fixed it calibrating using the wacom drivers, but as I said it doesn't matter how much I calibrate that zone always seems to be inaccurate. I don't think this is a hardware problem because as I said I had 2 surface pro (one with the 4200u processor and the other one with the 4300u) and both have this problem. There's a way to fix this? Or I just need to accept it? This is a pic of the problem.