A sensing device for enabling a user to interact with a computer system. The sensing device is operable in a cursor control mode and a substrate-interaction mode. The sensing device includes: a nib; a nib switch configured to effect a mode change between the cursor control mode and the substrate-interaction mode; an optical sensor for sensing coded data printed on a substrate; a processor for generating cursor control data or interaction data; and a transceiver for communicating the cursor control data or the interaction data to a computer system. The cursor control data initiates a cursor control response in the computer system, while the interaction data initiates a substrate interaction response in the computer system.