wrote:
different formulations all have varied dielectric constants, meaning
that the gauge could indicate 22 gallons one day and 18 the next; do you
want to bet your life that there's four extra gallons in the tank?

TheSmokingGnu

Ye Olde E6B and zeroing in on real fuel consumption at cruise gleaned
from actual flight should save the day (older planes not up to chart
performance, usually).

Well, even there you have significant challenges; you have to account
for the fuel in takeoff/climb (according to power/leaning), as well as
in descent, and you have to somehow figure out how much you've used in
taxi and runup. There are still large areas where the best you can do is
guesstimate at actual fuel usage.

Even then, unless you have a penchant for wingwalking, it's exceedingly
difficult to measure actual fuel usage in cruise without the fuel
gauges, which we have already established as really "best guess"
instruments anyway.

TheSmokingGnu