A room hygrometer is a device used to measure humidity. You get used to it measuring the temperature as well. Air humidity is an important factor in many fields, such as agriculture, construction, heating, ventilation, air conditioning (HVAC), etc. If the indoor humidity is too high, mold may appear. Some types of mold cause respiratory problems and other negative health effects for people who live or work in the environment. Additionally, mold that has penetrated the walls or ceiling of a structure must be removed for safety reasons