The quantity of most interest in understanding the mass is the binding energy, defined for a neutral atom as the difference between the mass of a nucleus and the mass of its constituents. This seems t...The quantity of most interest in understanding the mass is the binding energy, defined for a neutral atom as the difference between the mass of a nucleus and the mass of its constituents. This seems to show that to a reasonable degree of approximation the mass is a function of A alone, and furthermore, that it approaches a constant. This is called nuclear saturation.