the reason i said that the on board computers calculation of fuel economy is incorrect (lie)

is that from personal experience and as has been discussed before in this forum that is the case , it is highly optimistic in its calculations.

in my case the computer claims fuel economy of 8.1 litres per 100 (diesel) however if you do the calculations your self i get 9.1 litres per 100, or 9.4 per 100 when using the A/C.

i use my car for work and keep detailed records for tax purposes and can assure you that these figures are correct,

so again the onboard computer lies