Wexler, A., and W. G. Brombacher. Methods of measuring humidity and testing hygrometers. National Bureau of Standards, Circ. Sample Psychrometric Calculations 1. Find the humidity ratio of the air represented by point A by reading horizontally across to the vertical axis of the psychrometric chart.
Heating is represented by moving horizontally to the right from the initial temperature conditions.
On calm, clear nights the air cools by radiation, following a horizontal line to the left.