In many situations there is a need to simplify sensor simulations, for example in real-time simulations, electronic warfare simulations, or when the actual sensor has to deal with a large number of targets. The report presents a simplified method for simulation of radar tracking. By applying the mechanical definition of Centre of Gravity, on the radar cross sections a radar sensor has to handle, an effektive sensor model has been developed that gives possibility to handle large number of targets and electronic countermeasures. The implementation of this Centre of Gravity tracking method in the simulation model ChfDuel II (simulation of chaff deception against a tracking radar) and some simulation examples is presented in the report. A comparison between simulations using the ChfDuel II model and results from real radar tracking against a chaff dispensing aircraft indicates that the Centre of Gravity tracking method is a useful approximation in this situation. The method is a considerable simplification of reality and should therefore be used with care. Instead of modelling the construction of the radar sensor, the behavior of the sensor is modelled (generic model). However, it is possible to combine this method with more detailed sensor descriptions when needed.