Hygrometers provide an indication of the humidity of the vivarium. This has to be maintained at a level as close as possible to the natural habitat of the animal. Many health problems in all species are caused by maintaining the wrong humidity. It is vital that appropriate measures are taken to adjust the humidity to keep it at a suitable level, such as adding or removing containers of water with a large surface area, or regular use of a handheld mist sprayer on internal surfaces. Some products provide a dual reading for both temperature and humidity.