[NachtRitter]

I don't know exactly how the Scangauge II calculates it, but I like the options it presents... a 'trip' Average (If I've stopped more than 7 minutes, the Scangauge automatically resets the trip), a 'daily' average, and a 'tank' average.

Since I live at the top of a hill, I can easily coast out of my driveway all the way to the bottom of the hill (about .7 miles), using 0 fuel while still covering a distance... infinite MPG. During that time, the Scangauge shows nothing on the 'trip' display. Only when I start to actually use fuel does the Scangauge start to show some kind of FE numbers for the trip.

Of course, during the early part of a 'trip' or 'tank', small changes in my FE will affect the average. For instance, if I do start my car at the top of my hill and coast down in neutral, the FE avg will be HUGE! But once I get out on the road driving normally, it quickly drops down to a more realistic value.

Seems like you could take a similar approach using VBA... check first if there is any fuel consumed for the interval you're calculating, and only try calculating if some has been consumed. Otherwise show 0.00L/km. Once fuel has been consumed, then show the actual values... the more fuel consumed (and km traveled), the more accurate the FE calculation.