tide gauge

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A gauge for showing the height of the tide, particularly one continuously updated.

from the GNU version of the Collaborative International Dictionary of English

• n. an instrument for determining the height of the tides.
• n. a gauge for showing the height of the tide; especially, a contrivance for registering the state of the tide continuously at every instant of time.