This unit is an excellent compromise between less accurate, "consumer" grade digital thermohygrometers and highly accurate but complicated analog sling psychrometers. Measures humidity from 0 to 100% rH, with accuracy of ±4%. Measures temperature from -4 to 122° F (-20 to 50° C) with accuracy of ±1.8° F (±1° C). Resolution is 1° F, 1° C, and 1% rH. Data functions include Temperature, Humidity, Dew Point and Wet Bulb Temperatures, "Min/Max" and Data Hold settings. Requires 2 AAA batteries (included).