Two orthogonal encoders (not shown), which may be similar to encoders 146 and 148 for ball 104 (see FIG. 3), sense the rotation of ball 222 and send signals to a host computer. [0094]FIGS. 15A through 16B show embodiments which are similar to the embodiment of FIGS. 14A and 14B except that the second ball is in different locations in housing 102.