1. A method for operating a graphic user interface in a windowing operating system comprising the steps of: determining from information stored in the operating system a value representing a mapping of logical inches to real measurement units; determining from information stored in the operating system a physical size in real measurement units of a display device used to display the graphic user interface; asking a user viewing the display device to identify a displayed graphic image having a preselected dimension in real measurement units; displaying a plurality of graphic objects, wherein each of the graphic objects have a different size; asking the user viewing the plurality of graphic object to select one of the graphic objects; storing the size of the selected graphic object as a first user-defined size.