Hello, I measured color on different places on a fully white screen. When visualized on the CIE 1931 x,y plane, I got an area of size around 0.01. The distance between two closest shades of white (255,255,255 and 254,255,255) is around 8e-4. Accuracy of the colorimeter, i.e. the diameter of the smallest circle enclosing many measurements of same color at same place, is around 4e-4. So, variations of color on the screen is around 10 times more than the variation due to limited (8-bit per channel) digital representation. Who measured such unevenness of professional monitors, could you post your results? If it's common, doesn't calibrating process look like asking what is the weather in Africa? (where?!!) My monitor (not pro): CRT Samsung SyncMaster 797DF. Same result (0.01 variation) for LCD screen of IBM ThinkPad X40. Colorimeter: DTP94.