A sensing device is disclosed. The sensing device interacts with a surface having coded data thereon. The coded data is made up from tags. Each tag encodes a unique identity of the surface, and the location of that tag on the surface. The sensing device has an optical sensor for capturing images of the coded data on the surface when the sensing device is placed in an operative position relative to the surface. The sensing device also has a processor for processing the captured images to determine the unique identity of the surface and the operative position of the sensing device on the surface. A movement sensor for generating movement data is also included in the sensing device. A transmitter of the sensing device transmits indicating data to a computer system. The indicating data includes data regarding the identity of the surface, data regarding the operative position of the sensing device and said movement data.