If your car's odometer reads "Trip [A]" and shows different mileage, you probably need to reset the trip computer. There should be a button you can push to cycle through the different settings very near the odometer reading, usually on the dash. If you cycle through far enough, the car will display the correct mileage again.
The odometer is the way many people keep track of their car's mileage. It also determines the value of a vehicle when it comes time to sell. A car with lower mileage will often be worth more than one with more miles on it. That's why it's common for people to roll back their odometers when they're selling their cars.
Trip A and Trip B are the odometer's two trip meters. Trip A works in concert with the regular odometer to record mileage. The difference between the two is that trip A can be reset, while trip B cannot.
The information a trip computer provides can vary depending on the model of your vehicle. However, most will contain the following:
Fuel consumption: This will show the average amount of fuel the car consumes during a particular period of time. The information can also be used to calculate the distance-to-empty and may even indicate when it's time to refuel.
Other information: High-end trip computers can provide a wide range of additional features, including two drivers' average calculations, a stopwatch, and tire pressure information. This makes them a valuable tool for any driver.