Calibration method for a liquid system

A liquid system, comprising:

• a first reservoir filled with a liquid;
• a second reservoir filled with the liquid;
• a channel which connects the first reservoir and the second reservoir in a liquid-tight manner so that the first reservoir and the second reservoir are reservoirs that communicate with regard to the liquid;
• a capacitance sensor which is configured to measure electrical capacitance at one or more of the first reservoir or the second reservoir;
• at least one of:
• a differential pressure sensor for measuring a pressure difference between the first reservoir and the second reservoir;
• a light barrier which is arranged at a first known height at said first reservoir or said second reservoir and comprises a light source and a light sensor, or
• a capacitance barrier which is arranged at a first known height at said first reservoir or said second reservoir;
• and
• a control unit which is configured to;
• determine a filling level of the liquid in the first reservoir;
• measure, with the capacitance sensor, a first electrical capacitance at the first reservoir for the filling level of the liquid;
• set a different filling level in the first reservoir;
• determine the different filling level in the first reservoir;
• measure, with the capacitance sensor, a second electrical capacitance at the first reservoir for the different filling level;
• and
• determine a relationship between filling level and electrical capacitance based on the filling level and the different filling level in the first reservoir and the first electrical capacitance and the second electrical capacitance.