This hygrometer has a bimetallic mechanism and it's possible to calibrate it completely. You can use it as a rough indication for incubators, among others. The relative humidity is indicated as a percentage from 0-100. The humidity in an incubator depends on the kind of eggs and the extend to which the shell is porous. You can use this hygrometer as an indication an then check this indication by weighing the eggs regularly. In our assortment we have the very precise scales CS100 and CS500 as a solution for this. This combination is the best method to determine the humidity very accurately. An egg should loose 11-13% of it's weight during incubation. By calculating how much weight the egg should loose every day, you can determine whether you should adapt the humidity in the incubator. We only sell best quality hygrometers from the brand TFA from Germany.