A buoyancy compensator (or buoyancy control device, BC or BCD) is a piece of diving equipment worn by divers to provide:
life saving emergency buoyancy both underwater and on the surface.
the ability to adjust and control the overall buoyancy of the diver and the diver's heavy equipment allowing the diver to achieve neutral buoyancy, remaining at constant depth, or to descend or ascend in a controlled way.
Some types of buoyancy compensator also built around the diver's scuba set or are built into its harness.
