Haenni OWO Suisse 564 Psychrometer - Air Humidity Meter
This used instrument is in good cosmetic condition and comes in the original leather carrying case.
The Haenni psychrometer (aspiration psychrometer according to Assmann) has two thermometers (dry and wet-bulb) and a ventilator with a spring motor.
The reading is taken after moistening the wet-bulb thermometer with distilled water and ventilating for at least 10 minutes.
The instrument is suspended approx. 1.5 to 2 m above ground in the shade.