VIEWING ANGLE
The center of the screen should be lower than the eye height, so as to obtain a
viewing angle of about 25–35 ̊ below the horizontal (Hill and Kroemer, 1989). People
who sit in an upright posture prefer to look down rather than look up or look straight
ahead. In particular, looking up with the head bent back is a common cause of strain
and muscle fatigue in the neck.