Ohhhhhh ok I see now, I feel a little stupid now because it's exactly the same cross as the other frethand muted cords, but I didn't make the connection. Thank you very much for answering my question and giving me this little guide.
http://puu.sh/AwrAI/b553e9a0a4.jpg Hello I'm trying to learn "Gamma Knife" but I never saw theses "X" before, so I don't know what to do. Does anybody know what I'm supposed to do, please ?