The psychometric chart is a graph of the properties (temperature, relative humidity, etc.) of air. It is used to determine how these properties vary as the amount of moisture (water vapor) in the air changes.

• Dry-bulb temperature is the air temperature determined by an ordinary thermometer.
• Wet-bulb temperature reflects the cooling effect of evaporating water.
• Dew point temperature is the temperature below which moisture will condense out of air.
• Relative Humidity is a measure of how much moisture is present compared to how much moisture the air could hold at that temperature.