Halcyon Zero Gravity Sidemount SystemZero Gravity Sidemount System The ZG puts the buoyancy over the hips and along the sides of the rib cage where buoyancy is desired. The air chamber positioning gives the ZG a flat and streamlined profile on the back of the diver. The small and compact unit will pack nicely along with other gear in a traveling suitcase or dive bag for travel. The ZG is suited for double aluminum 80s and a wetsuit or small steel cylinders used with dry suits and heavier