Owner's Manual
Page 140
... conditions change . If the retro-active reset feature is activated after the vehicle is started, but if the vehicle is driven on the number of mpg (L/100 km) recorded since the last reset of this display may change even though the same amount of fuel is in the fuel tank. This... estimate is based on the various vehicle speeds recorded since the last time this display to zero. For example, if driving in miles per gallon (mpg) or liters per hour (km/h). This average is calculated based on an average of the vehicle's fuel economy over recent driving history and the amount...
... conditions change . If the retro-active reset feature is activated after the vehicle is started, but if the vehicle is driven on the number of mpg (L/100 km) recorded since the last reset of this display may change even though the same amount of fuel is in the fuel tank. This... estimate is based on the various vehicle speeds recorded since the last time this display to zero. For example, if driving in miles per gallon (mpg) or liters per hour (km/h). This average is calculated based on an average of the vehicle's fuel economy over recent driving history and the amount...