djhlady "fn+f4 Switches the screen image among display devices connected to the system.
For example, if a monitor is connected to the computer, fn+f4 alternates the screen image from computer display to monitor display to simultaneous display on both the computer and the monitor.
Most external monitors receive video information from the computer using the external VGA video
standard. The fn+f4 hotkey can also alternate images among other devices that are receiving video
information from the computer." from the user manual.