it comes from how they cheaply and simply implemented the fuel sensor.=20
i forget what the typical circuit and mechanical arraignment are, but
that's where the nonlinearity comes from, i don't think anyone planed it
that way, they may have realized that's what would happen, but didn't
care given that it basically works (on a plane of course you need
absolute accuracy since running out is really bad and to save
weight/fuel they often don't put in much more than they need for the
planed trip).  the accuracy problems are also from cheap uncalibrated
sensors and equally cheap meters that aren't particularly calibrated
other than usually setting the full scale and/or empty (interestingly i
once had a former state patrol car, it ran out of gas with a 1/4 tank
still left!  seems they'd diddled with it to help if someone stole the
car, i.e. they'd keep driving away thinning they still had plenty of gas
and then run out early, a very clever idea i thought though learning it
the hard way was annoying).  it just happens to turn out that you get
more resolution and stronger feedback that you need gas soon towards the
end.  i have however seen cars with fairly linear and accurate fuel
gauges so you really want to know how they work in the particular model
you are driving, with many cars E means E, not hurry up and get gas
within 10-20 miles, it can be a rude surprise.

"M. Adam Davis" wrote:
------
> Of course they don't.  Instead they use a deceptive scale - mine has
> markings at each 1/4, but is the tank half empty when it points to the
> 1/2 mark?  No, it's closer to 1/3 full.  It appears that they use a
> logarithmic type sensor with a linear display (or vice versa).  I
> suppose they assume people want more resolution the closer to empty the
> tank becomes, but for me I'd like to know that since I can go 240 miles
> on one tank then I have 0, 60, 120, 180, 240 at each mark.
--------

--=20
Philip Stortz--"In Germany they came first for the Communists, and I
didn't speak up because I wasn't a Communist.=20
Then they came for the Jews, and I didn't speak up because I wasn't a
Jew.=20
Then they came for the trade unionists, and I didn't speak up because I
wasn't a trade unionist.=20
Then they came for the Catholics, and I didn't speak up because I was a
Protestant.=20
Then they came for me, and by that time no one was left to speak up."
-- Martin Niem=F6ller, 1892-1984 (German Lutheran Pastor), on the Nazi
Holocaust, Congressional Record 14th October 1968 p31636.

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