From start to finish, the RG100 balance piston 1st stage delivers exceptional performance for all your dives. Coupled with the O.D.S. hose system, the balance piston delivers consistent, maximum airflow at vitally any pressure level and diving depth. A unique flow-through piston design ensures optimum flow, even under arduous diving conditions.  Recommended 2nd Stage: OC350, OC300, OC450, OC400  Advantages: reliable, easy breathing, high performance  Users: tech divers, sport divers