Tide gauge

From Glossary of Meteorology

tide gauge

A device for measuring the height of tide.

It may be simply a graduated staff in a sheltered location where visual observations can be made at any desired time, or it may consist of an elaborate recording instrument (sometimes called a marigraph) making a continuous graphic record of tide height against time. Such an instrument is usually activated by a float in a pipe communicating with the sea through a small hole that filters out shorter waves.