Dosing system for liquids

The liquid auxiliary dosing system includes a determining arrangement (38) for determining an operating variable in the operating of the dosing pump unit (14), characterizing and adjusting this. A comparison-judgment unit (42,44) is provided for comparing the operating variable with at least one reference value and for determining the operating condition of the dosing pump unit (14), based on the comparison result. In the comparison-judgement unit (42,44), a multiple of reference values is provided in the manner of a performance graph (K), for comparison with the operating variable.