The market now contains a bewildering variety of input devices for communication from humans to computers. This paper discusses a means to systematize these devices through morphological design space analysis, in which different input device designs are taken as points in a parametrically described design space. The design space is characterized by finding methods to generate and test design points. In a previous paper, we discussed a method for generating the space of input device designs using primitive and compositional movement operators. This allowed us to propose a taxonomy of input devices. In this paper, we summarize the generation method and explore the use of device footprint and Fitts’s law as a test. We then use calculations to reason about the design space. Calculations are used to show why the mouse is a more effective device than the headmouse and where in the design space there is likely to be a more effective device than the mouse.