Question

how is humidity measured?

Answer 1

Dry' air will contain water vapor with a VP which is less than the SVP at the given temperature. A device to measure relative humidity is called a hygrometer. The simplest hygrometer - a sling psychrometer - consists of two thermometers mounted together with a handle attached on a chain. One thermometer is ordinary.

Answer 2

we can measure the humidity using a hygrometer..