Quote Originally Posted by chuboy View Post
The trip computer polls every 100m or so and spits out a cumulative average fuel consumption for the whole trip up until that point. So right after you reset after filling up at the servo you are doing a lot of driving in 1st gear so average consumption for the distance you have driven since you reset is quite high... once you are on the highway your consumption is low and so you notice the average consumption decreases gradually until it eventually approaches your instantaneous consumption. Even though you use lots of fuel when in 1st gear, the distance covered is small so its overall effect on the average consumption is outweighed by the large distances and low consumption of highway driving. Of course if you never do highway driving and your sole use of the car is stop-start in 1st or 2nd gear, then the fuel consumption figure will not decrease as you have observed.

Also, the longer you have gone without resetting your trip meter, the harder it is to make the fuel consumption average change (since it is taking the average of all the fuel consumption figures since you last reset which may have been many thousands of kms ago).

It's all to do with the mathematics of taking an average I reset my Trip A about 20000 kms ago, the fuel consumption is a solid 8.5 L/100km which pretty much never goes up or down. Then I use Trip B to see my fuel consumption per tank.
Same here, the auto reset on fill-up function for the trip computer is genius!