is there a device that I can remotely hook up somewhere that will record my mileage when I drive my car?

I don't know if I'm really ready to start taking apart the dash and mess with the odometer and I want to know what kinda mpg I am getting because it seems a little on the low side.

Is there a GPS device that can record my distance every time I drive and record it until I reset it?

I have a GPS unit but it only records the distance I'm traveling if I program a location.

I just want something to be able to measure my mileage so I can calculate where I'm at.

If anyone knows of anything please chime in...

thanks

Jason

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1985 mercedes benz 300D turbo diesel
1998 VW GTI VR6
1996 VW GTI 2.0
1999 saab 9-3 turbo
1987 300sdl (sold)