Mark the vent (delivery) temperature on the vertical line.

Mark the ambient air (intake) temperature on the bottom line.

Draw a vertical line from the ambient air (intake) temperature mark.

Draw a horizontal line from the vent (delivery) temperature mark until it intersects the vertical line.

NOTE: The low side and intake temperatures should intersect in the shaded area within about 10 % of the measured humidity level. Any measurements outside the line may indicate the need for further inspection.