ah the answer then is it doesn't. Yes as you say I'll have to do the mental math. It is just rather frustrating since both the ship display and the fuel panels have range boxes, only the numbers stated in either are simply unrelated to the reality of the situation. I've hit a serious fuel crunch and had to get ships back to Earth arriving with vapour in the tanks....2 arrived with <2% fuel remaining.
It is even more complex when ships with different speeds are in a formation as the fuel is expended at the full rate even if the ship is moving at half the velocity. I'm not sure why Steve doesn't included a "Velocity_Current/Velocity_max" term in the fuel use formula and simply things.
Regardless, thank you I can stop looking for what isn't there.