One of the main reasons people dive is to interact with the underwater world. It can be as visually stunning as any landscape and offers the sense of weightlessness that is a welcome relief from busy surface lives. There is also the thrill of adventure, whether being carried by currents in drift diving or discovering unexplored areas.

Interest in the underwater world has driven divers to develop ever-improving methods for staying longer and deeper under water. Ancient manuscripts depict early divers gathering sea cucumbers and pearls and Herodotus (500 B.C.) tells of the sponge divers of Greece.

The modern self-contained underwater breathing apparatus, or scuba, is a key piece of equipment. This is a system that allows you to stay under water for a period of time limited only by the depth at which pure oxygen becomes toxic (and by your ability to hold your breath for that long). There are two basic systems: open and closed circuit. The former vents all exhaled air into the water, while the latter uses carbon dioxide absorbed rope soaked in caustic potash so that the diver’s exhaled gas is re-breathed without entering the water.

The other important pieces of scuba equipment are the scuba mask, scuba snorkel, and scuba fins. These are augmented by the BCD, which is often called a BC, or buoyancy control device. It looks like a backpack and contains air bladders that can be filled with compressed air to control your buoyancy, as well as pockets for storing tools and accessories.