The Kestrel 3500 Delta T wind meter takes all the great features of the Kestrel 3500 and adds in an additional useful reading- Delta T. The delta T is the spread between the wet bulb temperature (in degrees C). Delta T offers a quick guide to determining acceptable spraying conditions. For example, it is not recommended to apply pesticides when Delta T is above 10- a range of 2-8 is ideal. With the Kestrel 3500 Delta T, the calculation is done for you, accurately and simply. The unit incorporates barometric pressure correction in its wet bulb temperature calculation, ensuring accuracy even on low pressure days, at high altitudes, and in the very dry weather when Delta T monitoring is important. No other pocket weather meter offers this feature with this level of accuracy.