Humidity is a measure of the amount of water vapor in the air. Relative humidity, which is often what is measured when humidity is spoken of, is the amount of moisture currently in the air in ratio with the maximum amount of moisture that the air could hold at that temperature, and expressed as a percentage. A humidity gauge, also known as a hygrometer, is an instrument for measuring absolute or relative atmospheric humidity. A humidity gauge may also be used to measure the humidity in other contexts besides in the air. Italian artist and inventor Leonardo da Vinci is said to have built the first hygrometer in the 15th century, and English scientist and inventor Robert Hooke also made a notable hygrometer.
There are several different types of humidity gauge. One type is a psychrometer. A psychrometer includes a wet-bulb thermometer and a dry-bulb thermometer, which are compared to calculate relative humidity. Another type is a hygroscope, which shows changes in relative humidity, but not the degree of change.
A humidity gauge is employed for many different applications. A humidity gauge can be placed in the soil of sensitive plants, such as orchids, to allow a constant assessment of the soil temperature and humidity in order to assure the best growing context. A humidity gauge is characteristically employed to maintain an appropriate environment for several different kinds of pets. It is typically used by owners of hermit crabs, snakes, anoles, frogs, turtles, amphibians, lizards, tortoises, and other terrarium dwellers.
In assessing building comfort and safety, a humidity gauge may be used. Keeping humidity below 50 percent is said to both contribute to killing mildew and mold — or at least making it dormant — as well as leading to the death of dust mites, leading to less allergens in the air. It can also be an indicator for when a dehumidifier should be run. The humidity gauge is also part of a standard weather set, along with a thermometer and an anemometer. Many weather sets are stationary and hung in a house or in a protected location out of doors, but there are also portable weather stations with humidity gauges that are made to be carried in one’s pocket.
In other cases in which humidity assessment is important, such as cigar humidors and wine cellars, a humidity gauge may also be used. Special models of humidity gauges for humidors may have markings to indicate the ideal humidity range. Wine cellar humidity gauges can be part of or used in conjunction with a wine cellar management system.