The fact that calibrating it brings it back to a similar value, > indicates that most of the drift is the black offset (dark noise). > I used the white reference switch because it produced more expressive results (luminance difference in degrees), so I am not sure about the absolute luminance levels. Yes, the re-calibration bring the original X and Z coordinates closer to the first results. The black drift was bigger than the drift in the chroma. But the re-calibration didn't change the CCT, it monotonously increased during the full measurement set. (And I think the display was relatively stable after ~10 hours uptime.) And it certainly a temperature related thing because this effect showed monotonously decreasing effect. (But I think it's safer to wait two hours. One hour wasn't enough for me...) I will be a full day job at the end: Two hours acclimatization, high setup times (mentioned in the i1Pro thread) and the need for the adaptive mode with higher integration times. And a lot of black/white drift compensation measures, simply because it's a very long measure set anyway. :) And it reminds me to another question: You say that the default mode may gives us more coherent results because the adaptive mode works with random integration times. Can't we use constant (but user defined and high) integration times?