In most scuba sets, a buoyancy compensator (BC) or buoyancy control device (BCD), such as a back-mounted wing or stabilizer jacket (also known as a "stab jacket"), is built into the harness. Although strictly speaking this is not a part of the breathing apparatus, it is usually connected to the diver's air supply, to provide easy inflation of the device. This can usually also be done manually via a mouthpiece, in order to save air while on the surface, or in case of a malfunction of the pressurized inflation system. The BCD inflates with air from the low pressure inflator hose to increase the volume of the scuba equipment and cause the diver gain buoyancy. Another button opens a valve to deflate the BCD and decrease the volume of the equipment and causes the diver to lose buoyancy. Some BCDs allow for integrated weight, meaning that the BCD has special pockets for the weights that can be dumped easily in case of an emergency. The function of the BCD, while underwater, is to keep the diver neutrally buoyant, "i.e.", neither floating up or sinking. The BCD is used to compensate for the compression of a wet suit, and to compensate for the decrease of the diver's mass as the air from the cylinder is breathed away.