However, wet-bulb and dry-bulb temperatures are values easily measured, and a glance at Figure 2 (psychrometric chart) shows that lines of constant wet-bulb are parallel to lines of constant enthalpy, whereas lines of constant dry-bulb have no fixed relationship to enthalpy. Therefore, wetbulb temperature is the air parameter needed to properly size a cooling tower, and its relationship to other parameters is as shown in the Figure 3 diagram.