To know the magnetic state of a complex deviee, very often, the only solution is to measure the induction in a finite number of locations around the item. The difficult point is then to go back to the magnetisation from the measures. A model of magnetic sources is first searched for. The spheroidal harmonic expansion of mesurable field and the search of normal equivalent dipoles spreaded over the object surface are studted. Their advantages and drawbacks are very complementary, so a new model, synthesis of them is proposed. Then, the use of a Bayesian algorithm allows to indude in the projection of the measures on the mode!, al! the uncertainties and inconsistencies created by the imperfection of the measure. In return, only a confidence interval is available. Lastly, an analytical parametric study allows to know the performance of the algorithms. Particularly, the choice of sensors type is presented.
