A method of using a mobile device to determine a position of a print medium, the print medium configured to be printed on by the mobile device in a print direction, the mobile device including a printer, a first sensor and processing means, the print medium comprising a substrate defining first and second opposite faces, the first face bearing coded data indicative of at least one location, the method comprising the steps of: (a) using the first sensor to capture a first image of at least some of the coded data when the print medium is at a position within a media feed path within the mobile device; (b) using the processing means to decode at least some of the sensed coded data, thereby to determine at least one location; and (c) determining the position of the print medium based on the at least one location determined in step (b).