A cover is provided for use on a computer mouse having an outer shell and a mouse ball projecting from the shell. The second detector is preferably a position sensitive detector that provides accurate, rapid position information that can be used as feedback to stabilize the position of the pattern on the first detector. In addition, the DRAM cell only uses one field effect transistor device, has characteristics of the conventional 1T-DRAM, and has higher integration density. Also, impedance matching is readily enabled, thereby reducing a parasitic element. The top rim is sized to engage a bag having a resealable closure.