TIL: the optical mouse works by taking a picture of the desk surface and does Optical Flow with the previous capture to get relative position.<p>The result reminded me of the old Logitech Scanman handheld scanner. except that had a 1d light sensor (like a flatbed scanner) and a radial encoder attached a to a roller to advance the scan lines down and the user pulled it down. (kind of like a 1d mechanical mouse.) I had a ton of fun with that growing up.