KOB (see Gallery-KOB) noticed that the automatic gain control (ACG) doesn’t work as well in Europe. As pointed out in Noise from Electricity – Part 1 the ACG reduces any peaks caused by the electricity in the walls (60 Hz in the USA and a few other countries and 50 Hz in the rest of the world). KOB lives in Europe and if you look at his readings they do tend to have small peaks at around 50 Hz, for example “KOB eyes closed”, 5th second:
Luckily these peaks are small enough that they shouldn’t have much of an effect on the overall results. My understanding is that the Mindwave was developed in the U.S.A., and it could very well be that its ACG is more sensitive to the American 60 Hz, and less sensitive to the European 50 Hz.