How does a Regulator work?

Few pieces of sporting equipment carry more mystique than scuba regulators. Obviously, a scuba diving regulator allows a diver to breathe from a tank underwater. But how does a regulator transfer the high pressure air from the scuba tank to the diver’s lungs at a pressure that will not injure him? What are the differences between a piston and a diaphragm first stage? Curious? Check out the following videos: