Water level measurement on board to ensure the safety of the ship, used to determine the draft (draft, trim) of the ship's position. Typically, one measurement point is at the bow and the other at the stern. If the ship is larger, two additional measurement points are often added, one in the middle of the hull, one on the port side and one on the starboard side. In order to be able to accurately determine the hull position and draft, it is necessary to be able to accurately measure the water level.