I've recently driven a number of Japanese import mid 2000s Toyotas, and they have fuel consumption information on dash and on touch screen. There is a instantaneous consumption gauge (0-30km/l), then average fuel, range, average speed and something else. There is a button that appears to reset average speed, however I can't see a way to reset average fuel?

Someone guessed/suggested it's a rolling average? Anyone know. This must be a common setup as these were all quite different cars and models.