The Degauss switch corrects small patches of color distortion that can occur
on the screen. You should press the Degauss switch if, for example, you
notice that a small area in an all-red field of the screen seems to be
slightly off color, say, with blue. This situation is more likely if you've
left the monitor on for a long time or if you moved the monitor while the
power was on.
The switch is located just below the On-Off button on the back panel.
Pressing the Degauss switch makes the screen flicker for a few seconds as
the monitor corrects the colors in your display. When the image steadies, the
colors should be correct.