The HT30 Wet Bulb Globe Temperature (WBGT) meter measures the Heat Stress Index, or how hot it feels when humidity is mixed with temperature, air movement, and radiant heat. The meter can also detect individual temperature, humidity, and radiant heat, as well as monitor the impacts of direct solar radiation on an exposed surface using the Black Globe temperature sensor. An in/out function shows the WGBT value with or without direct sunlight exposure. Auto Power Off with override and an RS-232 interface are among the additional features. Comes with two AAA batteries.