The Dwyer RP3-NIST Thermo-Hygrometer Probe, Wireless, measures relative humidity, temperature, dew point, and wet bulb temperatures when combined with the Model UHH6 Universal Handheld. In order to protect the sensor in higher air flow ducts, the RP3NIST comes with a membrane filter. Factory calibrated replacement humidity sensors can plug directly into the RP3NIST without requiring additional calibration.