Digital integrated intelligence or di2: with programmed automatic motion at the touch of a switch the Dura Ace Di2 rear derailleur is quick, smooth and effortless, making for unmatched drivetrain efficiencythe rear derailleur is now the brains of the system with wireless connectivity to the shifters. It acts as the point the system is charged, provides Ant+ connection to 3rd party devises and replaces the handlebar junctionbutton on the derailleur for Di2 operations, and led light denotes synchronized shift mode, setting mode and charge requirementsprogrammed automatic motion at the touch of a switch makes this derailleur quick, smooth and effortless to shiftsynchronized shift designed, developed to choose the next biggest or lowest gear ratio irrespective of whether a gear change needs to be made by the front or rear derailleurthe removal of traditional mechanical cables in favour of electrical wires not only eliminates poor shifting caused by contaminates, corrosion and stretchinglow