1(underwaterdiving) The set of equipment required by a scubadiver to be at ease when submerged for extended periods of time. Modern equipment sets include tanks containing mixes of nitrogen in varied ratios with oxygen, a buoyancy control device, a first- and second-stage regulator (to allow the regulated flow of gas from the tank into the user's respiratory system), a wetsuit and accessories for heat insulation, fins for underwater propulsion, a mask (to see underwater), and a snorkel (for moving around the surface of the water without using up breathing gas). Many divers also choose to dive with a diving knife (in case of a tangle with a net, etc.), and night divers may also dive with a waterproof flashlight.