Microsoft uses BlueTrack technology across its line of mouse products – designed to work on any surface, except glass or mirrors. The fact that Microsoft's vaunted BlueTrack doesn't work on glass or mirrors provided Logitech responded with its own advanced laser tech, called “Darkfield” technology. Darkfield relies upon the individual dust particles found on a glass surface to track the mouse's position. In fact, if you are using the mouse on an exceptionally clean glass surface you'll have to wait a few minutes for it to find some dust before the mouse will work correctly. Logitech's Darkfield technology has no problem scrolling on glass provided it's at least 4mm thick.