The mercury reduction unit HovaMERC mercury reduction unit is used to generate elemental, mercury-containing test gas. It relies on the reduction of mercury chloride, which is generated in a gas vapor mixture with the HovaCAL® calibration gas generator. The heated reduction unit is connected downstream from the evaporator of the HovaCAL® such that there is a continuous flow of hot, humid mercury (II)-chloride-containing (HgCl2) test gas through the reduction material. At the gas outlet of the HovaMERC mercury reduction unit, the test gas comes out with a precisely defined concentration of elemental mercury (Hg°). The reduction material reacts with chlorine and hydrogen chloride, thus releasing elemental mercury. As a result of this process, the reduction material is consumed and must be replaced on a regular basis.