a highly sensitive instrument for the study of levels that is used in astronomical, geodetic, and other goniome-tric instruments. Level testers determine the scale spacing of the level (the angle at which the inclination of the axis of the level to the horizon will change when the bubble is displaced by one scale division), its dependence on temperature, and the constancy of spacing along the scale.
One important part of a level tester is a very precise micrometric vertical screw, which rests on an agate disk. The head of the screw has a calibrated circle. In field conditions, the scale spacing of levels is found by the Comstock method, without reading the level from an instrument.