1. A method for real-time calculation of state variables (x M ) of a process model on a process computer having a first calculating unit and a process interface, wherein the process computer is designed in such a manner that at least one state variable (x P ) of a physical process is recorded by the process computer via the process interface and/or at least one output variable ( y ) can be issued by the process computer for controlling the physical process, wherein the process model is calculated with an explicit integration method by the first calculating unit for determining the state variables (x M,e ) and wherein a second calculating unit is provided, the process model is carried out with the second calculating unit using an implicit integration method essentially simultaneously with the calculation of the process model with the first calculating unit, the state variables (x M,i ) of the process model calculated with the second calculating unit and the implicit method are used as a basis for correcting the calculations of the process model carried out on the first calculating unit and the state variables (x M,e ) determined in this manner with the explicit integration method are used as state variables (x M ) of the process model.