Abstract: An apparatus and method for operating a graphic user interface in a windowing operating system. A value representing a mapping of logical inches to real measurement units is determined from information stored in the operating system. A physical size in real measurement units of a display device is determined. A user viewing the display device is asked to identify a displayed graphic image having a preselected dimension in real measurement units. A plurality of graphic objects are displayed, where each of the graphic objects have a different size. The user viewing the plurality of graphic object is asked to select one of the graphic objects. The size of the selected graphic object is saved as a first user-defined size.