Thanks guys!
Yeah, the tube silo thing on the side houses the mouse wheel generator / battery. You can still pop the cap off to feed the little guy in there (charge the battery seperately).
You cant really tell from photos but the screen is set in the back of the box with a magnifying glass under the round bezel to bring the display out a little larger than it would have been. I wanted it to look like a view window on an old diving helmet.