MPG calculator?

[C.A.R.]

Too much effort and i dont do full fillups i put bits in here and there so it is never accurate

Then you will never get an accurate reading mate, because you have no 'constant' value.

You could buy the most expensive equipment in the world and still you wouldn't get an accurate mpg reading, because all trip computers require calibration. Even OEM dashboard read-outs need calibrating properly (especially if you make any changes to the car or haven't serviced it in a while)

Oh and if Tom is reading, yes your Golf definitely got 65mpg despite defying all logical explaination...