The average subject ratings with respect to ease of use (1:diffi-
cult/7:easy), learnability (1:difficult/7:easy), efficiency (completing
the tasks fast and accurately was: 1:difficult/7:easy), fun
(1:dull/7:fun), fatigue (1:tireing/7:not tireing) and overall preference
are illustrated in Figure 5, together with standard deviations.