There's a distinct difference between time at indicated airspeed (which is what calculations based on fuel consumption per unit time are based around) and the g

There's a distinct difference between time at indicated airspeed (which is what calculations based on fuel consumption per unit time are based around) and the ground distance you'd cover. Ground-dwellers - that is, most readers - are comfortable with miles per gallon (or, say, litres per hundred kilometres), but it's a useless number as an aircraft spec.