Fuel consumption should be measured in SWG.
This is obvious if you think about it - the dimensions of SWG are 1/area, which is the same as length/volume, ie how far do you go for a given amount of fuel, good so far ...
... but what makes it even more obvious is to think of the vehicle proceeding along a wire made out of fuel and consuming it as it goes.
[SWG: Standard Wire Gauge, for anyone who didn't build their own electronics in the days before this metric stuff came in.]