Abstract: A fill level measuring system for the liquid content of a tank, with a fill level sensor (10, 50) for generating a signal proportional to the height of a point of the liquid level, an additional volume flow sensor (14, 52, 56) for generating a signal proportional to the inflow or outflow, and an indicating instrument (28). To compensate for systematic errors with high-frequency portions, for example due to air turbulence in the case of an airplane, and low-frequency portions, for example due to position changes (climb/descent; upward run/downward run for a motor vehicle) it is proposed to direct the signal of the fill level sensor (10) through a low-pass filter (12) and the signal of the volume flow sensor (14) through a high-pass filter (18), and to sum up both signals before the indicating instrument (28).