A method of determining a registration offset in a hard copy apparatus, the apparatus comprising a pen arranged to mark a print medium and a sensor arranged to detect marks on the medium along a sensor path, the method comprising the steps of: marking a alignment pattern on the medium, the pattern being at least partially located along the sensor path; detecting the position along the sensor path of a portion of the pattern; and, determining a distance by which the pattern is offset from the sensor path in a direction substantially perpendicular to the sensor path, the pattern being configured such that the defected position is indicative of the offset distance.