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).

IIRC on similar thread(s) the idea was put forth that the regs only
require the indicator to indicate properly when full and when
empty ... don't know where that would be in the regs (if in fact it
is); maybe part 23?