A psychrometric chart is defined by five distinct lines. Learning to distinguish them is the key to mastery.

Maintain a laminated copy of a sea-level psychrometric chart at every HVAC workstation. Practice plotting three states daily for one week to build fluency.

Moving downward on the chart. This usually happens during cooling when the air hits the saturation curve and "sheds" water. Humidification: Moving upward on the chart.

Measured in pounds of moisture per pound of dry air (or grams per kilogram). It tells you exactly how much water vapor is in the air, regardless of temperature. C. Relative Humidity (RH)

This is the curved line hugging the left side of the chart. It represents 100% Relative Humidity . This is the point where air is completely saturated with water vapor.

Diagonally sloping lines pointing down toward the right. The Scale: Read along the curved Saturation Line.