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measurement of ocean depth. The earliest technique involved lowering a heavy rope or cable of known length over the side of a ship, then measuring the amount needed to reach the bottom. Tedious and frequently inaccurate, this method yielded the depth at only a single point rather than a continuous measurement; inaccuracies arose because the rope did not necessarily travel straight to the bottom but instead might be deflected by subsurface currents or movements of the vessel.