Q. Dew point meter- is it measured or calculated?

One can use a hygrometer to directly measure the dew point or one can calculate it from the relative humidity.Measurement: A dew point hygrometer is an instrument used to precisely measure the dew point of a given sample of air. It's a bit difficult to understand so let's simplify it. A dew point hygrometer consists of a mirror a light beam and a light detector in a sealed chamber. Calculation: With the help of a sling psychrometer one may determine the relative humidity of a given environment and use that information to derive the dew point. An attached thermometer sits at the top of a metal rod or psychrometer that is about 6 inches in length.