In my 2008 manual 5spd. Hyundai Accent, 2013 automatic 6spd. Elantra, & 2016 manual 6spd. Elantra, computer MPG data has always been more accurate to calculated "miles driven/gallons used", while using 100% ethanol-free gasoline. 10% ethanol blend is NOT what the engine computer is calibrated to measure, but 100% gasoline is the calibration standard.
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