A method of maintaining a status of a product item is provided. The product item includes an associated interface surface which has coded data including a plurality of coded data portions indicative of the product item's identity. The method includes, in a sensing device, sensing at least one coded data portion, generating indicating data indicative of the product item identity therefrom, and transferring the indicating data to a computer system. The computer system is responsive to the indicating data to update product status information stored in a data store. Each coded data portion is indicative of the respective position. The method further includes, generating in the sensing device and using the sensed coded data portion, indicating data indicative of at least one of a position of the sensed coded data portion on the interface surface and a position of the sensing device relative to the interface surface.