A question related to Car average mpg display correctness I suppose, but say if a piggy back chip (e.g. http://www.dieselandpetroltuning.co.uk/) was added to a diesel car with trip computer, would the trip computer take into account the extra fuel injected via the remap/chip, or would the increase in fuel consumption be ignored and make the trip computer less accurate?
Sites selling chips such as these claim
Improved MPG for high mileage drivers
but to test these claims, would you have to measure the relative consumption manually rather than use the relative values reported by the trip computer before and after fitting?