[Alan Roehrich]

Grains of water is most often used as a reference to relative humidity, it simply tells you how much of the available air is actually water. You cannot burn water, effectively anyway.

You really have to make some runs and see what affects your particular combination, and to what degree. Not all engines react the same, especially if you consider the state of tune. The best way to use a weather station is to create and use an Excel spread sheet, so that you can accurately record each weather condition, and how it affected your car, and then go back and determine how much each condition moves your ET and MPH for a given amount of change.