A sidebar to the article “Meet the mouse,” published in Personal Computing, issue 3/1983, pp. 104.

The Xerox optical mouse uses no moving parts to detect its motion. As the mouse slides over an array of dots on a special pad, a tiny lamp illuminates the dots and an image is reflected by a mirror and focused through a lens onto an integrated-circuit sensor chip. The chip recognizes the pattern of dots before the mouse moves, remembers that pattern, and compares it to the new pattern of dots it sees during and after the mouse’s movement. In this way it determines the direction of motion and the distance traveled. Finally, it translates the information into digital form that tells the computer how to move the cursor on the screen in a corresponding manner. Buttons are used as on the mechanical mouse.