This Fieldpiece SDP2 Dual In-Duct Psychrometer is a genuine Fieldpiece Psychrometer perfect for HVACR professionals. This meter is made and designed to measure air conditions such as humidity, and then give you a live digital reading; it does this with its dual thermometers. How you operate this Fieldpiece SDP2 Dual In-Duct Psychrometer is by exposing the dry thermometer to open air to read the air temperature, and then using the wet bulb by dipping it in the water to read its temperature. By getting these two readings you can then find the relative humidity in the area, by calculating the difference between the two temperatures. This Fieldpiece SDP2 Dual In-Duct Psychrometer has a Back lighted dual display feature that will show you the wet and dry bulb readings, the dew point, and RH% so you can have the most accurate information on the jobsite. This Tool comes with the outstanding protection of the Limited Fieldpiece Warranty. Fieldpiece is a company that is a company that?s been around for since 1990. They have made it their goal and mission to improve the tools that HVACRs use, to make their jobs easier and our homes more efficient.