[en] The mathematical model of an accelerator can be used to control its operation and also to simulate its behavior. Part of the model is the conversion between the computer controlled digital setpoints of the magnets and the actual field acting on the average particle in the magnet. We are using tune, dispersion and chromaticity measurements to calculate this conversion, thus calibrating the model rather than the magnets themselves. this is one way to include effects, not taken directly into account in the model. The model has to be calibrated at different beam momenta, and possibly at different beam intensities