A robot for marking an interface surface is provided. The interface surface has coded data identifying a plurality of locations on the interface surface printed thereon. The robot comprises: an image sensor for sensing at least some of the coded data; a processor for generating indicating data using the sensed coded data, the indicating data comprising data regarding a position of the robot on the interface surface; communication means for transmitting the indicating data to a computer system and receiving instructions from the computer system; a steerable drive system for moving the robot over the interface surface in response to movement instructions received from the computer system; and a marking device for selectively marking the interface surface in response to marking instructions received from the computer system.