I disassembled a broken GretagMachbet Eye One Display 2 http://logout.hu/cikk/home_cinema_color_management/kalibralas_profilozas.html (The text is Hungarian, but pictures talk for themselves...) I always thought it uses three filtered and one unfiltered sensors. That's normal. There's room in the design for a fourth filter, but it's not > used. > > I'd imagine that there are two screws underneath the label. > >