In city driving 13 would not surprise me based on my experiences. Measured over short distances I see the computer display 8-10 mpg in the city. It settles down to about 15 with mixed driving, which is really 13.5 - 14 as measured. I suggest ignoring the computer until you have some factual data to work with. I suspect the error, like mine, is fairly consistent. Once you know how far off it is, it becomes useful.