A computer program embodied on a computer readable medium, said computer program configured to control a controller to: output, to a display driver, data for causing the display driver to drive a display of a printing apparatus to display, in a first area of the display, a plurality of images including a first image, wherein the plurality of images are representative of a plurality of respective different types of label data field, and to display a second image representative of the appearance of a label medium occupying a second area of the display that is different from the first area; and in response to receiving, from a selector, information comprising data representative of an operation of the selector by a user to select the first image and data representative of a position within the second area, output, to the display driver, data for causing the display driver to drive the display to display a revised version of the second image representative of the appearance of the label medium; wherein the revised version of the second image comprises a label data field of the type of label data field of which the first image is representative, and wherein the label data field comprised in the revised version of the second image is located at a location determined in dependence on said position within the second area.