The Extech HT30-NISTL Wet Bulb Globe Temperature (WBGT) measurement considers the effects of temperature, humidity and direct or radiant sunlight. It can also determine Heat Stress Index which measures how hot it feels when humidity is combined with temperature, air movement, and radiant heat. Black Globe Temperature (TG) monitors the effects of direct solar radiation on an exposed surface. An in/out function displays the WGBT value with or without direct sun exposure. Additional features include Auto Power Off with override and a built-in RS-232 interface. It includes Limited NIST Certification.