The whirling hygrometer is made out of two thermometers mounted on a frame which rotates around a handle, so it can be whirled in the air by hand.

This hand held whirling hygrometer is used for obtaining wet and dry bulb temperatures.

Bacharach type sling Psychrometer for indicating percent relative humidity on the basis of the wet bulb-dry bulb thermometer principle. The plastic case of the instrument is equipped with conversion scale for calculating the percent relative humidity.