A user interface control for scrolling a display of computer program data during retrieval of computer program data includes a track, a bar overlying the track, and a thumb button movable along the bar to scroll the displayed data. The size of the track indicates the total amount of data being retrieved, and the size of the bar varies to indicate the progress of the data retrieval. Thus, the ratio of the size of the bar to that of the track indicates the ratio of available to total data. The computer program data is displayed in a display area allocated to the computer program, and the size of the thumb button (compared to a corresponding size of the track) indicates the ratio of the amount of data displayed in the display area to the total amount of data being retrieved.