The principle of the frequency modulated continuous wave radar level gauge is that the radar emits electromagnetic waves at the top of the tank, which are reflected by the medium and received by the radar. The frequency difference δ f between the received signal and the transmitted signal is proportional to the distance R to the surface of the medium: R=C (velocity) * δ f (frequency difference)/2/K (frequency modulation slope). Since the speed of light C and the frequency modulation slope K are known, the frequency difference δ f can be calculated to obtain the distance R from the radar installation position to the material surface. Then, by subtracting the spatial distance from the radar to the material surface (referred to as the air height) from the known total height of the tank, the height of the material level can be obtained.