Measuring instruments are tools used to measure physical quantities such as length, weight, temperature, pressure, and sound. An ammeter is a device used to measure electric current in amperes. A GAUGE is an instrument used to measure the pressure or level of a liquid or gas. An ohmmeter is an instrument used to measure electrical resistance in ohms. A sextant is an instrument used to measure the angle between two objects, such as the sun and the horizon. A thermometer is an instrument used to measure temperature. A BAROMETER is an instrument used to measure atmospheric pressure. A seismograph is an instrument used to measure and record seismic activity. A METER is a unit of length equal to approximately 39.37 inches. An altimeter is an instrument used to measure altitude. A GAGE is a device used to measure the thickness of a material. Sonar is an instrument used to detect objects underwater. Calipers are instruments used to measure the distance between two points. RADAR is an instrument used to detect objects at a distance. A RULER is an instrument used to measure length. Calipers are instruments used to measure the diameter of an object.