Measurement of the moisture or water vapor in gas can be expressed in terms of volumes, weights, moles, pressures or temperatures. The wide variety of terms for the amount of water vapor leads to confusion in the field of psychrometry because psychometric charts or tables are required to convert from one set of units to another. This confusion is further aggravated by the fact that it is also necessary in evaluating the quality of the moisture to take into consideration other parameters such as dry bulb temperature, absolute pressure and composition of the gas.