Ford Mercury Villager 1997 Owner's Manual page 31

Instrumentation
INST ECONOMY
Your instantaneous fuel economy is the fuel economy you get at
any particular moment. For example, you can see what your
fuel economy is in heavy traffic or on the highway.
Factors such as braking, acceleration, and road terrain affect your
fuel economy.
To display instantaneous fuel economy, press the SELECT button
until the menu displays INST ECONOMY. Your vehicle must
be moving for the computer to calculate a fuel economy greater
than zero.
AVG ECONOMY
The average fuel economy is an overall average of your fuel
economy taken from the last time the reset button was pushed.
The computer takes an average of all the types of driving you have
done since the RESET button was pressed (highway, city, heavy
traffic), and figures out the average fuel economy. You can calculate
your average fuel economy as often as you like. For example,
you can calculate the average fuel economy for each tank of fuel
or for every day.
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