I am quite new to the psychrometry and the study of humidity, and I'm currently learning about the dry-bulb wet-bulb thermometry. As far as my understanding goes, the wet bulb is connected to a source of water (by a moist cloth or cotton swab) and the evaporation of the water to the air around it lowers the temperature to get the wet bulb.
I can understand the concept here, but I believe I would need the heat capacity of the bulb to know the exact temperature drop in the wet bulb compared to the dry bulb. However, different thermometers may have different heat capacity and may show different wet bulb temperatures. How is this mitigated? How is the wet bulb temperature a constant value for a given relative humidity and dry bulb temperature despite the various heat capacities that may exist for the various thermometers used to measure the temperature?