"NoSpam" wrote in message ...
Is there a way
to accurately measure the fuel in the tanks while the aircraft is on the
ground (using some "mechanical" measuring tool/gauge)?

Yes, using a dipstick calibrated *for that aircraft*. This is quite
accurate w/in the range it can measure (for example, when my dipstick
reads 0 on each tank, I have between 0 and 14 gallons of fuel left.

Is there a way to
accurately measure the amount of fuel in the tanks while in flight?

Not of which I'm aware. As you note, fuel computers measure fuel
flow, but don't account for fuel loss due to, say, leakage around
an improperly sealed gas cap or sump valve.

A friend of mine has bought some digital fuel gauges (a combination a
several digital engine instruments -- but I forgot the manufacturer's name).
Using these fuel gauges, you "calibrate" the instrument/gauges by leveling
the aircraft (both "wings level" and "pitch/flying attitude level") and
starting with 0 gals of fuel in the tank, then adding one gallon at a time,
wait a while for the fuel to settle, then take an electronic reading, add 1
gal of fuel and repeat the process until the tanks are full. How accurate
is this method? (personally I do not know how accurate this is, but would
like to know from someone with experience using these instruments...)

The method of adding 1 gallon and taking a reading on the ground is
accurate enough -- it's one way of calibrating a fuel dipstick.

I'm not sure how accurately it would translate to monitoring fuel in
flight -- the pitch attitude for level flight will vary so much
depending upon the atmosphere, the W&B, airspeed, and so forth.
It seems to me the design of the fuel tanks and the placement of
the gauge would be critical to accuracy, but I'm unfamiliar with the
technology used to make what you call an "electronic reading". That's
the point I'd want to investigate, though -- how much do the readings
I get with this wonder differ if I change the plane's pitch?

Cheers,
Sydney