Presented by: http://www.weraceshimano.com/xtrdi2
One of the most unique features of XTR Di2 is the new Synchro Shift option. XTR Di2 has undergone over 20,000 test kilometers. This extensive test period allowed Shimano engineers to closely analyse the most efficient gear combinations for riding. With Synchro Shift enabled, it is possible to control both derailleurs with just one shifter. The front derailleur reads the position of the rear derailleur and automatically operates the front shift to position the gears in the most efficient gear and best chain line so the rider never has to worry about front shifting and correction shifts again.