Based on the internal acceleration sensor I could create images/drawings just moving the hand and "paint".
Using hand gesture like, rotate the hand in circle and I have the drawing of a circle. I want a rectangle I have to move the hand and drawing virtually a rectangle.
If it's too heavy the Smartphone( and this could be happend) and with faster gesture, the smartphone can fly .... you can use the PEN incorporated. And you will draw virtually in the air and the acceleration sensor will transmit in real time the position/coordinates to the tablet/Catchbook.
Using slow motion gesture with the Smartphone in hand the line it will be thinner but moving slowly it will be thicker.
In order to erase everything I have to shake it stronger and the drawing/"painting" is clean.