Shimano Dura-Ace R9160 Di2 aerobar shifters use a single button design and are intended to be used in Shimano's "full synchro shift" mode (mode 3). In fully synchro shift mode, the single Di2 buttons only shift the rear derailleur, either up or down, and the Di2 computer decides when to shift the front derailleur based on optimal front and rear gear combination. Front shift points can be customized in Shimano's eTube Project App.