Anyone know how to alter the algorithm that determines your actual MPG.

[leadhead]

On the Rover 75 I recently had, it was possible by pushing the manual trip reset button for a certain number of seconds, to get into the electronics of the car. It was possible to see "live" things like the temperature the thermostat opened and closed, fuel tank levels(had 2 tanks), Country code and lots of other stuff...The one I am interested in here is an algorithm which was adjustable to correct the on board reading of the fuel MPG. I check my mpg at every fill up. I always fill the tank to the brim and have a spreadsheet that works everything out for me, the problem is, my reading differs from the one given on the cars display, and I would like to correct it. I would imagine that originally all cars algorithms for this measurement were set at "1"...as idealy if you got 60mpg and multiplied it by the algorithm, you actually got 60mpg....but I would think that none of them were perfect, so for instance if your on board display said 60mpg but from a lot of brim to brim readings you actually got 66mpg....(on the Rover) I could alter the algorithm from its setting at "1" to a new setting of "1.1" which meant it multiplied its 60mpg by 1.1 to give you your actual mpg of 66.

Anyone know anything about this algorithm....