I recommend calibrating with Active LED on. If you do so, you have to defeat the dimming by using 1% windows with a 100% white background. You can set HCFR's pattern generator to use those. Larger windows and/or darker background will mess up the gamma. Use "WLED" for correction pre-set. Good luck, and let us know your results.Apologize if this has already been discussed but I can't search thread on the mobile version of this site. What size windows are to be used for calibration of the M55-C2 and M60-C3? Got my sets and plan to calibrate them using Colormunki and ColorHCFR.