I don't agree with that last assumption. The reason. I can drive and create a display where the green points on the 15 minute graph are all is significantly HIGHER or LOWER than the average reported in with the white line. I have a picture of that case posted somewhere on this site. The only way that can happen is if the 2000 data points includes points that are not on the 15 minute graph that bring the average up or down. there is obviously no requirement that they can't work with more points than they show in the graph.

My guess is that the average represents the average of the last 33-1/3 hrs driving. Why 33-1/3? If you have 2000 points taken 1 per minute you have 2000 minutes and 33-1/3 hrs.

Also I'd like to point out they picked 2000 points for some reason of their own.... There is no need for a 2000 point limitation. Its not a matter of having enough "memory". You don't need to store all 2000 points to create an average. In order to create an MPG average all you have to do is create a running total of miles traveled (one storage location) and gallons consumed (another storage location). You only NEED two storage locations to find the average MPG. If its 2000 points it was chosen for some specific reason. Probably as a running average so it would give you an idea of the trend of your RECENT driving.