Dry bulb (regular) air temperature is in the scale at the bottom. Relative humidity is in the curves. Trace up from 20 C until you get to 30%, then go from that point straight to the right to the edge where it gives you humidity ratio.
At 30% RH, air has an absolute humidity of 4.5 grams of water per kg of air.
At 40% RH, air has an absolute humidity of 6 grams of water per kg of air.
