This very useful accessory, used by most divers, allows you to control and choose the level of depth in diving.

The sub inflating or deflating the tube connected to the cylinders modifies the volume of the gav and therefore the whole volume of the sub + gav set. This decreases or increases the total mass / volume ratio that affects the hydrostatic thrust and therefore allows to obtain respectively a positive set-up to go back up or down to go down gently.

By adequately dosing the air, the structure is reached and maintained, and therefore the desired depth without having to work too hard to counteract the weight of the ballast.