Well, after figuring out in another thread what reserve fuel is I can be more precise. Right at the moment, to know what part of fuel I can use for actual mission, before RTB Bingo takes me out of the loop, I need to:
measure distance from home base, (DIST)
check out ac fuel consumption per minute at cruise at max alt, (CONS)
check out cruise speed at max alt, (CRUISE)
check out reserve, (RESERVE)
check out total fuel remaining, (TOTAL)
After this, fuel before Bingo is given (or at least should be, don't know algo used by sim) by following expression:
TOTAL - (DIST/CRUISE)*60*CONS - RESERVE
Very straightforward procedure. So it will be nice to have it reported somehow by sim.
And yes, I am aware it will be changing minute by minute, as ac is burning fuel and going further from base. Another reason, it would be nice to have it reported.