Tide gauge

A tide gauge is a device for measuring the change in instantaneous sea level, including periodic tides and long-term sea level rise, relative to a vertical datum. It is also known as a mareograph, marigraph, and sea-level recorder. When applied to freshwater continental water bodies, the instrument may also be called a limnimeter. Stream gauges may record water level, discharge, or both. In general, a water level sensor may be used in arbitrary bodies, such as reservoirs or a tank.