odometer

I have a 94 Chevy Caprice Classic, with a digital odometer. When I get in the car, it reads 130909. I will drive about 10 miles and it reads 130919. Well if I cut the car off and cut it back on, it reads 130909, as if I didn't drive the car. I am trying to figure out what could be the cause of this. My trip odometer works fine by the way.