The Rolling Average Fuel Economy (RAFE) is set (at the factory) to look at the last 1000 km.Over the course of my last 10 fill-ups (always 10-11 gallons), I've had mine read from 1-3 mpg higher or lower than actual. At least 8 of those fill-ups, the computer is indicating higher than the actual calculated mileage.
In that regard, mine seems to be quite accurate. When I drive to "30 miles to go", I have put in 11.8-11.9 gallons.The thing that's alarming is how fast the "Miles to go" part of the display drops as the tank gets closer to empty. I have driven several miles on "0 to go" and then put ten gallons of gas in to fill it.