eudiometer-measuring instrument consisting of a graduated glass tube for measuring volume changes in chemical reactions between gases. gauge, gage-a measuring instrument for measuring and indicating a quantity such as the thickness of wire or the amount of rain etc.graduate-a measuring instrument for measuring fluid volume; a glass container (cup or cylinder or flask) whose sides are marked with or divided into amounts.gravity meter, gravimeter-a measuring instrument for measuring variations in the gravitational field of the earth.og-measuring instrument that consists of a float that trails from a ship by a knotted line in order to measure the ship's speed through the water. measuring rod, measuring stick, measure-measuring instrument having a sequence of marks at regular intervals; used as a reference in making measurements.