The DSG dual-clutch gearbox is unlike a conventional automatic transmission. Two independent gearboxes are connected under load to the engine in turn, depending on the current gear, via two drive shafts. An output shaft assigned to each gearbox applies the torque to the driven wheels via the differential gear. Clutches and gearboxes are operated hydraulically by the gearbox mechatronics (a combination of mechanics and electronics). The electronic transmission control unit, sensors and hydraulic control unit form one compact unit. The control unit uses information such as engine speed, road speed, accelerator position and driving mode to select the optimum gear and to determine the ideal shift point. The control unit then implements the shift commands in a sequence of precisely co-ordinated actions. Each change takes less than four-hundredths of a second. DSG can be used manually, via the Tiptronic gearlever.