While it uses temperature measurements (dry bulb and wet bulb) to calculate humidity, the final unit of measurement is typically relative humidity (RH), expressed as a percentage (%).

Here's why:

* Dry bulb temperature: Measures the actual air temperature.

* Wet bulb temperature: Measures the temperature of a wetted bulb as air passes over it. The water evaporates, causing a cooling effect.

* Difference between dry and wet bulb temperatures: This difference is used to calculate the dew point (the temperature at which water vapor in the air condenses into liquid water).

* Relative humidity: Determined by comparing the dew point to the air temperature. It represents the ratio of the amount of moisture present in the air to the maximum amount of moisture the air can hold at that temperature.

So, while a sling psychrometer uses temperature measurements, its primary output is relative humidity.