very crude maths, but...
does this sound right?
today i travelled 250 miles on 3/4 of a tank,
for (roughly) 3/4 of a tank it cost me £25
ergo, 10 miles per £1
at 87.9p per litre of fuel, i work it out at £3.99 somethin per gallon) (4.55 litres) meaning £4 = 40 miles
40mpg over a 250mile average
is my maths right?
ofcourse it wasnt as rounded as that, but thats about as close as i can recall from the clocks.