This HW30-NISTL multi-function stopwatch displays a digital up/down timer, temperature, humidity and heat index. The heat index measurement shows how hot it feels when humidity is combined with the actual temperature. Ideal for use in hot weather conditions. Additional features include a 12/24-hour clock, stopwatch, 30 lap/split memory and programmable alarm. HW30-NISTL Humidity/Temperature HeatWatch comes with lanyard, battery, and operating instructions. Includes a limited NIST traceable certificate.