Most second stages are fitted with a flow vane of some description in order to control how air flows around the second stage housing. This is called the venturi effect. Some of these vanes are fixed at a pre-determined angle, most can be manually adjusted by the diver but Atomic Regulators go further.
The vane is there to help prevent unexpected free flows, especially during water entry and in shallower depths when the regulator is more sensitive or whilst the second stage isn't being used. It works by directing some of the air that flows through to the mouthpiece back into the housing towards the diaphragm, cancelling out the negative pressure that initially built up behind the diaphragm to assist the valve opening and helping to force it shut again. The amount of effect that it has depends on the angle of the vane, deflecting more or less air backwards, often identified by 'pre-dive' and 'dive' positions on the control knob.
Atomic took a different approach to the problem. Firstly they made the whole thing automated and secondly, rather that rotate the vane they made it move in and out to create turbulent air that flows everywhere or directed air that goes straight to the mouthpiece.
The Atomic Automatic Flow Control (AFC) eliminates the manual adjustment normally needed to regulate the venturi effect as you dive deeper. A computer-designed airfoil inside the mouthpiece is connected to a pressure-sensing diaphragm, allowing the airfoil to change position with response to depth. The AFC is the reason Atomic regulators breathe with a comfortable natural feeling at any depth. The video below shows you how this works.