The psychrometer is a device used to measure the
Relative Humidity (RH) of the air.
Relative humidity is the ratio of
(the amount of moisture in the air, here and now)
to
(the amount of moisture the air could hold at this temperature) .
Being a ratio, it has no units. It's just a naked number, always
less than ' 1 ', and usually expressed as a percent.
I believe the answer is evaporation
hope it helped<span />
