1| Relative humidity thermometers or psychrometers are used to measure the humidity or vapor content of the air.

2| They consist of a dry bulb thermometer (conventional thermometer) and a wet bulb thermometer (surrounded by a cotton cover soaked in water).

3| The relative humidity of the air is determined from the temperature difference between both types of thermometers.

4| Made of plastic, it presents a direct conversion table for reading relative humidity from the temperature difference recorded by dry bulb and wet bulb thermometers.

5| With red colored liquid.

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