Altimeters

right|thumb|Diagram showing the face of the three-pointer sensitive aircraft altimeter displaying an altitude of . Reference pressure of about 29.92 [[inHg (1013 hPa) is showing in the Kollsman window.]] An altimeter, or altitude meter, is an instrument used to measure the altitude of an object relative to a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.