Tangent Element Bundle of Tk, Mf, Kb & Bt Panels A bundle of all 4 panels from the Tangent Element range: Tk, Trackerball panel. Mf, Multifunction panel. Kb, Knob panel. Bt, Button panel Ultra slim, aluminium construction 5 x white OLED displays Controls: 4 x 3-way trackerballs. 12 x optical shaft encoders, with reset. 45 buttons USB connection with no separate PSU required