Sorry G-S if the way I express economy upsets you, but I can look at it both ways. If someone tells me they get 15 kpl and I know the size of the tank it is easy to work out 15 x 22 = 330 k's on the other hand if it 6.6666666666666666666666666667 litres per 100 k's I just go 7x3 21 litres 300 k's, close enough does it really matter after all it is only grade 4 math.