The humidistat works on a very simple principal. Any variation in the relative humidity level will cause an electrical resistance between the two sets of conductors on the sensing element. Because there are alternating metal conductors, the amount of electrical resistance between the two can be accurately predicted based on the relative humidity. This resistance is measured by the relay amplifier. When the electrical resistance indicates that the humidity level is below the desired level, the relay will turn the humidifier on to raise the humidity level. When the proper humidity level is reached, judged by the electrical resistance between the conductors, the relay will turn the humidifier off.