The psychometric probe according to ISO 7726 has a dry bulb (direct to environment) and a wet one (permanently wet).
Both probes are located in the centre of a controlled air flow (ventilation) and offer you the parameters of dry bulb temperature and wet bulb temperature (both ventilated). These two parameters allow us to calculate with good accuracy the relative humidity and all derived parameters such as absolute humidity, dew point and enthalpy of the air.