Wet and Dry Bulb
To measure a temperature, we can measure the dry bulb or the wet bulb temperature. For frost protection, the wet temperature is important. When the relative humidity is 100%, the wet and dry temperatures are equal. The lower the humidity, the bigger the difference.
In the table below, we show the differences between the two, according to the humidity.
The top row (red) shows the dry temperature, the left column the RH (relative air humidity). The black numbers in the table indicate the wet temperature.
Example: a dry temperature of 0 °C and a RH of 50% result in a wet temperature of -2,9 °C.