Yes when I fill mine up I only drive about a mile to the fuel station. Then I get a range of 400 miles. If I then drive on to the motorway and do a steady 50 mph the range goes up to 420-430 ish.. So it obviously depends on the state of the engine, how hot it is etc, and what speed you are doing. If I could maintain that speed for 430 miles then it would probably be correct. In fact it may go up higher if I reduced the speed to say 45 mph. But sooner or later I think I would fall asleep at the wheel. I certainly couldn't drive for that length of time to try it out. So I believe the gadget.