MG MG3 Owner's Handbook Manual page 28

INSTRUMENTS AND CONTROLS
Instantaneous Fuel Consumption
Instantaneous fuel consumption is automatically calculated
by the car. When the car is stationary or the vehicle speed
is very low, 'Instantaneous Fuel Consumption' will display
"—MPG".
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Average Fuel Consumption
Displays the average fuel consumption of the distance
travelled since last reset (the average fuel consumption
is calculated by dividing the amount of fuel used by the
distance travelled). The consumption value can be reset
at any time to record the average fuel consumption for a
particular journey or driving conditions. The average fuel
consumption shall be calculated after the engine starts
when the vehicle speed exceeds 3 MPH.
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Note: The fuel consumption is related to driving style,
road conditions, load, tyre pressures, vehicle electrical
appliance application and maintenance levels etc.