This demonstration video goes over the features of the Hollis DC4 212 & 221 Balanced Regulator. The DC4 212 Regulator comes with an over-balanced first stage achieves superior performance by increasing your air flow the deeper you go and a pneumatically balanced second stage. The DC4 212 Regulator features an environmentally sealed first stage provides greater reliability, less maintenance and higher performance. The 212 second stage comes with a "diver adjustable" air flow and a "diver adjustable" venturi to prevent unwanted free-flow. Whereas the 221 second stage comes only with a "diver adjustable" venturi to prevent unwanted free-flow. There are easy grip controls even while wearing gloves.