The chart is a grid where you can find the heat index temperature by looking at the air temperature and relative humidity. For example, the NWS says if it's 96 outside and the humidity is 65% ...

You then compare this to a relative humidity chart to check the humidity level. PUPIL: The wet bulb temperature was two degrees Celsius. PUPIL: And the dry bulb was four degrees Celsius.

The chart is a grid where you can find the heat index temperature by looking at the air temperature and relative humidity. For example, the NWS says if it's 96 outside and the humidity is 65% ...