I have the PA301W and the 2690WUXi and use Spectraview for calibration. For 2+ years they have worked perfectly and matched each other exactly in image brightness, color, and contrast. Suddenly they don't quite match - the 2690 is slightly, but noticeably, warmer than the other even right after a calibration. I believe I do the calibration properly - shield from stray light, allow to warm up, etc. What could be the cause of this? Running Windows 7.