On the Speedometer Cluster:
You can see that there is a place that displays the cars actual mileage, and there is a place where it displays the mileage you have driven since you last reset/zero'd out the tripometer/trip miles.
What I was trying to say is that, I would go to the gas station, fill up my tank, and reset the trip mileage. Once I ran to empty, I would go to the gas station, fill up, and record the mileage on the trip meter. Lets say I went 200 miles according to the trip meter on my last fill-up... Well, according to the actual cars mileage meter, I went 250 miles. Lets say it went from 171,250, to 171,500 miles...
Does that make any sense this time? For some reason my trip miles are not consistent with the cars actual miles, so instead of relying on the trip meter for how many miles I have driven, I now rely on the cars actual mileage, and just record it every time I fill up... I hope this helped you understand what I was trying to say.