(v.) To limit the electron beam in a cathode-ray tube (CRT) to scan within the boundaries of the display. This reduces the normal size of a video image by as much as 20 percent. To ensure that the complete image is always visible within a display area, it is advisable to check the boundaries of an image in underscan mode. Computer monitors usually operate in underscan mode, but the underscanning feature is available only on professional-quality NTSC video monitors.
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