The temperature of the wet bulb thermometer at equilibrium with a constant flow of ambient air at a rate of 2.5 to 10.0 meters per second.
The temperature of the wet thermometer bulb in a wet and dry bulb hygrometer. The wet bulb is surrounded by wet fibres and evaporation of water from the fibres cools the wet bulb. The rate of evaporation depends on the relative humidity of the air.
The most accurate way of measuring relative or absolute temperature is to use two thermometers, one of which is kept wet by a pure water wick surrounding the bulb. Except at 100% humidity, the wet bulb will always indicate a lower temperature than the dry one. The conversion from the two temperature readings to either humidity is done by either tables or a mathematical formula.