Thought I'd share what I've learned about compatibility between the Shimano Flight Deck and the company's 105 levers. The 5500C levers, which are fully compatible with the Flight Deck cyclocomputer are marked "FLIGHT DECK" on the front of the levers themselves. They also have button nubs on the center facing aspects of the hoods. The 5500 levers, which are partailly compatible with the system (according to Shimano) do NOT have "FLIGHT DECK" on them.