n. Any instrument for ascertaining or testing pressure.n. An instrument for showing the compressibility of water or other liquid, and the degree of such compressibility under varying pressures.n. An instrument consisting essentially of a vertical tube inserted into a water-main, to show the pressure of the fluid at that point, by the height to which it ascends in the tube of the piezometer.n. A sounding-apparatus in which advantage is taken of the compression of air in a tube by the pressure of the water at great depths to indicate the depth of the water.n. An instrument for testing the pressure of gas in the bore of a gun.n. An instrument for measuring the degree of resistance of the tissues of the body.