> the tablet itself has additional capacitive sensors. Inductive, actually, which is why the stylus doesn't need to have a big fat tip. Wacom also make a styl

> the tablet itself has additional capacitive sensors. Inductive, actually, which is why the stylus doesn't need to have a big fat tip. Wacom also make a stylus for the iPad, which obviously has to be capacitive rather than inductive. I think it has batteries in it and sends tip pressure information to the iPad over Bluetooth. (How the inductive sensing works: You have some conductive loops behind the display, and in the pen there is a ferrite rod with a conductive coil around it together with a capacitor to make a resonant circuit. You pass an alternating current at approximately the resonant frequency through some of the loops; it couples to the pen circuit by electromagnetic induction, the pen circuit resonates, and for a short time it produces, by induction again, a signal in all the other conducting coils behind the display. How much signal depends on the position and angle of the coil in the pen. If you have enough loops behind the display you can work out where the pen tip is accurately enough to draw with it. The capacitor in the resonant circuit is variable and adjusted by the tip pressure, and small changes in the resonant frequency produce phase changes in the signal that comes back, so you can measure the tip pressure too. Similar technology is used in some interactive whiteboards.)