Monitors are very prone to interference from magnetic fields, even the earth’s natural magnetic field. The earth’s magnetic field is always changing, thus it has a constant influence on the monitor. Color purity for example will change. In order to reduce these effects every monitor has a degauss circuit that helps keep the colors pure and the geometry correct.
There is a coil of wire that goes around the picture tube just under the plastic near the front of the monitor. This is the degauss coil. When the monitor is turned on it will automatically degauss itself by sending a large current though this coil of wire. The degaussing circuit uses a thermistor to taper off the degaussing current over a period of a few seconds. Tapering the current off prevents the degaussing process from actually creating a residual magnetic field in the metal parts of your monitor instead of eliminating them.
Chief Hardware Engineer