A buoyancy engine, including an upper casing, a lower casing, and a manifold separating the upper and lower casings. The method balances recall and precision for the target class. The mechanisms, in response to a determination that a locally cached copy is present, determine whether the locally cached copy is a latest version of the shared resource. Alternately or in addition, the tracking device may include a battery that provides power to the tracking device and is recharged by the power receiving device.