This German made hair hygrometer has a large easy to read face that makes it simple to keep track of the relative humidity in incubators or breeding facilities. This is the hygrometer distributed by, and recommended for, Grumbach incubators by Grumbach/ProCon. These units provide a high degree of accuracy, and are reliable and easy to maintain (instruction sheet included). When not in use , store in an area where the relative humidity remains reasonably high. Roughly 3" by 3".