A hygrometer or hydrograph is a tool used to measure the degree of humidity, or other gas. The electric hygrometer consists of two electrodes spiral-wound. If applied to these electrodes an alternating voltage, the tissue is heated and part of the water content evaporates. At a defined temperature, a balance between evaporation by heating the tissue and absorption set aguto ambient moisture lithium chloride, a highly hygroscopic material. From these data sets accurately the moisture.