This paper reports on the experimental evaluation of a Graspable User Interface that employs a "space-multiplexing" input scheme in which each function to be controlled has a dedicated physical transducer, each occupying its own space. This input style contrasts the more traditional "time-multiplexing" input scheme which uses one device (such as the mouse) to control different functions at different points in time. A tracking experiment was conducted to compare a traditional GUI design with its time-multiplex input scheme versus a Graspable UI design having a space-multiplex input scheme. We found that the space-multiplex conditions out perform the time-multiplex conditions. In addition, we found that the use of specialized physical form factors for the input devices instead of generic form factors provide a performance advantage. We argue that the specialized devices serve as both visual and tactile functional reminders of the associated tool assignment as well as facilitate manipulation due to the customized form factors.