A method of enabling a user to instruct a computer system to perform an operation via an interface surface and a sensing device. The interface surface includes an interface, the interface including visible graphical information and substantially invisible coded data. When the sensing device is placed by the user into an operative position relative to the interface surface to designate at least some of the graphical information, it senses indicating data indicative of the operation using at least some of the coded data. The graphical information designated is at least partially indicative, to the user, of the operation. The operation indicated by the indicating data is then performed in the computer system.