We present two studies to assess which physical factors of various input devices influence 3D object movement tasks. In particular, we evaluate the factors that seem to make the mouse a good input device for constrained 3D movement tasks. The first study examines the effect of a supporting surface across orientation of input device movement and display orientation. Surprisingly, no significant results were found for the effect of physical support for constrained movement techniques. Also, no significant difference was found between matching the orientation of the display to that of the input device movement. A second study found that the mouse outperformed all tracker conditions for speed, but the presence or absence of support had no significant effect when tracker movement is constrained to 2D.