A stiff, straight spar is allowed to pivot about an anchor on the seafloor.he location of the bottom with respect to the top is then determined by measuring the tilt of the spar and computing the offset of the bottom relative to the top. The straight member uses its internal buoyancy to remain erect and stable while the weight of the anchor keeps it in place on the seafloor. The top of the spar is tracked by shore stations while the tilt and heading of the spar is monitored by an instrumentation system. Simultaneous readings of the shore instruments and the spar's tilt and heading indicators allow direct determination of the anchor location relative to the shore. An air ballast control enables the apparatus to be easily maneuvered on the ocean bottom by divers or on the surface and an internal plumb bob system allows calibration of the overall system.