Replacement outdoor air sensor for Auto-Trac humidistat system. Is also used as an outdoor air sensor on certain Aprilaire thermostats. This sensor has a value of 230.6 K ohms at -30 degrees Fahrenheit, 11.9 K Ohms at 70 degrees Fahrenheit and 5.9 K Ohms at 100 degrees Fahrenheit. Its resistance goes up as the temperature goes down. Probe Length 2" - Wire Length 33 1/2"