A method of recording a transaction relating to an item, said item comprising a product contained in a package, said package having an interface surface containing information relating to the item, the interface surface having disposed thereon coded data indicative of an identity of the item and of coordinates of a plurality of locations of the interface surface, the method including the steps of: marking the interface surface using an optically imaging pen having a marking nib; sensing at least some of the coded data in the vicinity of the pen; generating indicating data using at least some of the sensed coded data, said indicating data comprising data regarding the identity of the item and positions of the pen relative to the interface surface; and transmitting the indicating data to a computer system.