Chevrolet 2007 Monte Carlo Owner's Manual page 188

Trip A and Trip B
Press the trip/fuel button until TRIP A or TRIP B
displays. This display shows the current distance
traveled in either miles (mi) or kilometers (km)
since the last reset for each trip odometer. Both
trip odometers can be used at the same time.
Each trip odometer can be reset to zero separately
by pressing the set/reset button while the desired
trip odometer is displayed.
The trip odometer has a feature called the
retro-active reset. This can be used to set the trip
odometer to the number of miles (kilometers)
driven since the ignition was last turned on. This
can be used if the trip odometer is not reset at the
beginning of the trip.
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To use the retro-active reset feature, press and
hold the set/reset button for at least four seconds.
The trip odometer will display the number of
miles (mi) or kilometers (km) driven since the
ignition was last turned on and the vehicle
was moving. Once the vehicle begins moving, the
trip odometer will accumulate mileage. For
example, if the vehicle was driven 5 miles (8 km)
before it is started again, and then the retro-active
reset feature is activated, the display will show
5 miles (8 km). As the vehicle begins moving, the
display will then increase to 5.1 miles (8.2 km),
5.2 miles (8.4 km), etc.
If the retro-active reset feature is activated after
the vehicle is started, but before it begins moving,
the display will show the number of miles (mi)
or kilometers (km) that were driven during the last
ignition cycle.