Those were simply range numbers if you had a fuel consumption gauge and was able to maintain a given speed while drawing a certain amount of fuel.
"IF" you could maintain sucking only 3gph at 37mph you would be getting 12.3mpg, multiply that by your available fuel then you would come up with your distance able to travel.
This is probably the thread that got me to do the graph or vice versa.
http://www.wellcraftv20.com/communit...hlight=numbers