Underscan means that the active video area appears in a rectangle centered on the screen with a black surrounding area. This ensures that the entire active video area always is displayed on all monitors. However, most monitors or televisions will cause some of this video to be lost beyond the edges of the display, so the entire image will not be seen. Choose Super VGA from the dialog and reboot your system. If your monitor is a VGA type, you can try the following cable pinouts.
Vendors have different image quality specifications.
There may be significant differences between Apple monitors and the wide range of VGA monitors. A cable wired as follows may allow many different brands of NTSC monitors to work on a Macintosh Centris or Quadra. I would advise you to test the monitor on one of these machines prior to purchase to see if it meets your expectations. By grounding pin 4 and pin 7 to pin 11, the Macintosh Centris and Quadra CPUs are told that an NTSC monitor is attached. The shell of the card connector connects to the sleeve of the phono-plug.