https://www.mccoys.com/shop/p/9855602-052303-30/bestair-hg050-6hg050-hygrometer
Measures indoor air humidity levels while showing optimal comfort area without the need of batteries. Reduces static electricity, which causes problems with electronic equipment. Helps sooth dry, itchy skin, throats and coughs. Also hydrates woodwork, furniture and houseplants. Use with any brand of humidifier.