Dalton's Law of Partial pressures is the basic principle for measuring water vapor or humidity. When you understand how we arrive at the basic measurement of the amount of water vapor in the air, you will have a better understanding of how to make a better measurement.

We discuss how the partial pressure of water vapor and the saturation vapor pressure work together to define relative humidity. When you can picture this concept, you can start to put together the pieces of each parameter you wish to measure.

Humidity Conversion Formulas from Vaisala

A podcast by Bruce McDuffee and Steven Santoro of Vaisala