If the
screen is positioned to one side, users will have to rotate their heads each time they
refer to the screen and again as they look back at their documents or keyboard. This
layout can also cause twisting of the upper body. Delleman (2004) has reported a
study by Hünting et al. (1981) that showed that VDU operators who twisted their
necks beyond 20º showed a higher incidence of neck and shoulder disorders.