This high-performance Regulator boasts an balanced first Stage coupled with a pneumatically balanced second Stage. The smooth, quiet breath is sure to enhance your diving enjoyment. Designed for water temps above 50F/ 10C the Comfort-Brite mouthpiece, with its patented Bridge virtually eliminates jaw-fatigue compatible with EAN40 out of the box. First Stage: the first stage is a balanced diaphragm type that offers consistent performance from start of dive until end of dive, regardless of depth. 1 HP port and 4 MP ports are available Available in yoke only second Stage: pneumatically-balanced second Stage results in smooth, easy breathing The large purge button on the At20 is easy to operate even with thick gloves. The integrated venture control Provides a performance boost at depth while preventing unwanted free-flow at the surface.