A robot adapted to operate in association with an interface surface having disposed therein or thereon coded data indicative of a plurality of reference points of the interface surface, the robot comprising: movement means to allow the robot to move over the interface surface; a sensing device which senses at least some of the coded data and generates indicating data indicative of a position of the robot on the interface surface; communication means to transmit the indicating data to a computer system running a computer application, and to receive movement instructions from the computer application; and, a marking device adapted to selectively mark the interface surface in response to marking instructions received from the computer application.