The Air Humidity Meter WB 20 SD is designed to capture WBGT-values（綜合溫度熱指數）, the Black-Globe Temperature（又稱黑球溫度計）, humidity, air temperature, wet-bulb temperature, and the dew point temperature indoors as well as outside. The Air Humidity Meter WB 20 SD has been developed for an objective rating of working places under extreme weather conditions. Objective criteria for the determination of an adequate level for physical activity outdoors can be valuable in industrial environments, since clear standards assure relevant actions. The US military developed the WBGT as a basic for their training camps, but since then the WBGT principle has been extended to work places and sports activity locations. The WBGT index is useful to develop guidelines for work breaks and limitations or preventions of intense activity. The Air Humidity Meter can read temperature and dew point values that can be stored onto a memory SD card. In case the conditions change, an acoustic alarm goes off.