In regards to the pump gallon
In regards to the pump gallon display accuracy, here in MA, our inspector of weights and measures certifies the accuracy by law. Do you know something different?
In regards to basic accuracy, I have kept track if the variation between indicated MPG and calculated MPG over 10,000 miles in my Mazda CX-5. On the average, the indicated MPG is about 6% higher than the calculated (miles / gal) MPG.
Again, the question is WHY? Technical or marketing?
Who Knows?