A couple of thoughts on the aFCD inaccuracy... 1 - It is a running average of fuel used and distance travelled since last reset of the gage. I find that they are accurate if you drive "only city" or "only highway", but they start to stray when mix some optimal 50mph highway travel with an hour of city slogging. Add in either of the two extremes and the gage will be off by more than a couple of mpg. 2 - The tank in the Accent is small, and when you're over 50mpg, half a gallon of gas is good for 25 miles. Adding fuel at another gas station whose pump kicks off a half a gallon early or late will result is a slight overfill/underfill that is much more dramatic when you're talking about lots of miles and relatively few gallons. 3 - At 58mpg, being off 5mpg is the same inaccuracy as a gage that reads 29mpg and is off by 2.5mpg, or a gage that reads 14.5mpg instead of 13.3. In short, you never want to trust the aFCD as your actual gas mileage. The correct figure is miles driven divided by gallons added. The aFCD is useful as a running scorecard for how you're doing, but it won't usually match up with true mpg. In my Elantra, I find that the aFCD is about 4% over, but the odometer is almost 4% under, which means that it's fairly accurate if I adjust for the odometer offset.