A monitor located at a high level is a source of discomfort and, in the long run, can cause musculoskeletal problems in the neck and shoulder area. Occasionally monitors are placed on top of the hard case or CPU. This finding allows one to extend the visual zone downward by another 15 degrees (an acceptable visual zone) for a total of 45 degrees (see Figure 2). On the other hand, looking downwards, that is, lower than 15 degrees below the horizontal, was not reported as particularly fatiguing. Numerous field studies among people doing intense visual work indicate that looking upwards (above the horizontal) is tiring. Such a location creates a preferable visual zone of 30 degrees (+ 15 degrees to -15 degrees from the normal line of sight).
Therefore, for comfortable viewing of images on a computer screen it is probably reasonable to place the monitor at about 15 degrees (or slightly lower) below the horizontal line. People engaged in visually demanding tasks limit their downward eye movements to about half of the whole available range of 60 degrees. Experimental findings range from about 15 degrees to almost 30 degrees. How far downwards, however, is not clear. Researchers agree that at rest, the eyes naturally assume a straightforward and downward cast (see Figure 1) line of sight.
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