A number of studies have developed various models to account for the speed/accuracy tradeoff in aimed movements. Reductions in performance are believed to be associated with the modifications of the visual and motor scale, demonstrating limits on visual and kinesthetic resolution, respectively. Alternatively, the visually displayed speed of the movement may impair performance by reducing the ability of the visual system to discern and correct for small trajectory errors in the fast moving cursor; while conversely, the speed of the hand could deteriorate functioning by increasing the neuron motor noise and subsequent movement variability. The index of difficulty predicts the difficulty of a task by simultaneously capturing the effects of visual scale, physical scale, or some combination of both. In a series of three studies, visual and motor scale were either held proportional to each other, or varied independent of one another via manipulations of the control-display ratio (gain), across four experimental sessions in four different directions of approach (left-right, up-down). Performance was assessed on several temporal, distance, kinematic, and error measures. In terms of the speed/accuracy tradeoff, the results indicate that overall movement time varied as a function of both visual and motor scale, in which amplitude affected the time in the primary phase, and perceived visual tolerance affect the timing of the secondary phase of the movements. Constant, variable, and root mean square error all increased with physical velocity and motor scale; while, angle of approach exhibited a biomechanical effect on error and movement time. As the mass of the limb increased with movements performed in depth, the error and movement time both decreased. Implications for movement control theory and human factors are discussed.