The fuel economy calculation is impacted by the inaccuracy of the speedometer/odometer. I have verified by several methods that the speedometer reads about 7% high. The speedometer reads 75 mph and actual speed is 70 mph. That same error applies to the odometer. So every 10,000 shown on the odometer only accounts for actually traveling 9300 miles. I complained to Lincoln with no acknowledgement of the issue. Why would they, their warranty coverage runs out at 7% lower mileage!
So if the mileage calculator uses the odometer (highly probable), it will give you a reading about 7% high. I don't rely on it!