This Demonstration shows how to read a psychrometric chart (also known as a humidity chart). Select the relative humidity (green curves) and the dry-bulb temperature ( axis) using sliders. Unchecking the "relative humidity" box removes the labels for the relative-humidity lines. Check the boxes for "enthalpy" (blue) and "specific volume" (purple) to display lines of constant enthalpy and constant volume, respectively. Check the box for "temperatures" to display dashed black lines that point to dry-bulb, wet-bulb and dew point temperatures that correspond to those values at the black dot. When the "temperatures" box is checked, move the mouse over each dashed line to identify which temperature it corresponds to. All temperatures are read on the axis. Check "display values" to see a table of the values obtained from the chart for the selected point; only the moisture content and the values whose boxes are checked are displayed. The values per kg are per kg of dry air.