Please can someone explain why fuel is still dispensed in units of volume whereas aircraft fuel guages display the mass of the fuel. The volume of fuel is completely irrelevant because the amount of internal energy it contains depends on the mass of the fuel and not the volume. Most modern aircraft have an instrument that measure the mass flow rate of fuel to the engines so why can't modern fuel bowsers also measure the mass flow rate being delivered to the aircraft? This would negate the problem of temperature errors/variable specific gravities.