How does the cost of ad-blue make up the cost against the mpg on the R470?, i mean is paying for the ad-blue the same as say a non ad-blue truck that is 1 mpg worse?.
If you’re light you hardly use any adblue at all (and it will dilute as much as 50/50 with water no probs on a Scania) so I would say on average the adblue costs about £10-15 pw.
So yes it does offset the savings a bit but hey it’s a 16 litre V8. . 
dont use the trip computer to see what your mpg is… make note of the mileage when u fill up… then when you re-fill take note of how many km/miles you have done and how many litres you have used… then just divide the litres (gallons) by how many miles you have done… simples 
Well I bought the truck that was mentioned in the OP , a 2006 R470 in November 2007 .its been a reliable motor and consumption wise it averages around 9 mpg on the work Im currently on…gotta agree with somethinggood on the trip computer , mine is always between 1.5 to 2 mpg out . Ive always worked on the adage that my fuel costs should be a third of my turnover for the week and this truck has kept me at or close to that figure since I have had it .