All of Apple's displays activate the degauss coil each time the monitor is powered on. The display can be degaussed by turning it off and powering back up again after waiting 15 minutes to 1/2 hour. After the waiting period, the display will degauss at power-up.
Generally speaking, in comparison to leaving a display on all the time with a screen saver, it's a good idea to power a monitor off and back on occasionally. This will activate the degauss coil to help remove any residual magnetic fields that may reduce CRT performance.
If the degauss coil has failed, magnetic fields may build up around the CRT causing purity and color shift problems in the display. The magnetic fields would be quickly noticed in the display indicating a failure and the need for service. The degauss coil and circuitry components are very reliable and failures are rare.
The older Apple High-Res RGB has a degauss button on the back of the display. Even with a degauss switch, this unit cannot activate the degauss coil any more than about once every 15 minutes to half hour.
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