The functionality of a conventional mouse is extended to provide an extended number of simultaneously adjustable user interface parameters employing one or more user-removable modules. In an embodiment, a user interface for controlling an external device, such as a computer, includes a first user interface sensor configured with a housing. This first sensor generates a first plurality of signals responsive to movement of the housing relative to two orthogonal axes. A compartment is configured with the housing and is sized to receive the user-removable module. This user-removable module contains a second user interface sensor, which generates a second plurality of signals responsive to user manipulation. Output is provided responsive to signals generated by the first and second user interface sensors. In another embodiment, the housing of an extended functionality mouse itself serves as a module removable from a compartment provided in another physical device.