Patent ID: 8063881

Claim:
An apparatus, comprising: an optical motion sensor; a user interface member; and a surface member coupled to the user interface member, the surface member operatively coupled to move over the optical motion sensor, the optical motion sensor to detect a fixed reference point on the surface member, wherein the surface member includes a first reflective area having a first reflectivity and a second reflective area having a second reflectivity, and wherein the first and second reflective areas comprise: horizontal lines superimposed on a checkerboard pattern having alternating blocks of the first reflective area and the second reflective area, wherein the horizontal lines have the second reflectivity when superimposed upon blocks of the first reflective area and have the first reflectivity when superimposed upon blocks of the second reflective area; and vertical lines superimposed on the checkerboard pattern, wherein the vertical lines have the second reflectivity when superimposed upon blocks of the first reflective area and have the first reflectivity when superimposed upon blocks of the second reflective area.