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Magnetization and Degaussing
While not really a characteristic of the CRT, this subject is related to it and I needed to put it somewhere, so here it is. :^) The image quality of the monitor, especially the color, can be adversely affected if the internal components become magnetized. This can happen from exposure to a magnetic field (by putting a magnet such as that in a stereo speaker near the monitor's surface) or through physical shock to the CRT, and sometimes even by something as simple as changing its orientation. Magnetization manifests itself through splotches of color on the screen, especially in the corners.
The process of eliminating magnetization on a CRT is called degaussing (the unit of measure of magnetic inductive force is the gauss, named for mathematician Karl Friedrich Gauss). Most modern CRTs today include built-in degaussing circuits. Some have a manual switch to activate the circuit, some do it automatically and some offer both as an option. The degaussing circuit uses a coil of wire to neutralize magnetic fields within the CRT.
If your monitor has a manual degauss button, you can use this to degauss the monitor if you ever have magnetization (color) problems. Just don't do it too many times in a row or you could risk damaging the circuit. When the degauss is engaged you'll hear a buzzing sound and the screen image will appear to vibrate for a few seconds; then you'll hear a click, the buzzing will stop and the screen will return to normal. Many monitors do this automatically when you turn them on, as a sort of "preventive maintenance" measure. If you hear the tell-tale buzzing and click in the first five seconds after turning on your CRT, that's the degaussing circuit in action.
Sometimes magnetization won't go away after a degaussing. If your monitor automatically degausses each time it is turned on, sometimes the best course of action is to ignore the color impurity and wait for a week or two to see if over time, multiple degaussings during power-on cycles will eliminate the problem. The other option is to use a manual degausser, which is a special demagnetizing device that is moved over the surface of the CRT (from the outside of course) to eliminate magnetic fields.
Warning: Manual degaussers
produce magnetic fields that can be damaging to data stored on magnetic media. Keep them
well away from floppy disks and hard disks. It is also a good idea to just generally keep
magnetic media away from your CRT.
Next: Monitor Power and Safety