Some people have asked why is there an electrode placed on one hand in our DC measurement even though we are measuring the super slow brain activity. The reason is this particular protocol was proven in 1982 by prof. Iluchina from the Institute of Human Brain in St Petersburg, Russia. Basically, to register DC potential you need at least two electrodes: active one- placed at vertex or frontal lobe, and a reference one - placed on a distant part of the body (so could be on the leg too). The measured signal is the difference in potential between the active and the reference electrode. It is assumed, that potentials at each point will influence registered signal with the same strength, but in different direction. Therefore, the best is to have a reference, which potential will have minimal influence on brain signal registered under active electrode. The thenar is such a reference point.