The paper presents an analysis of the distribution of the magnetic flux in an eddy current braking device. The analysis is based on a non linear finite element computation of the magnetic field combined with an analytical or numerical evaluation of the eddy distribution in the conducting slab. The paper describes the way in which the eddy current distribution leads to the definition of a power loss factor, which allows the determination of the electromagnetic torque. Particular attention is brought to the numerical problem caused by the velocity vector which lead us to use a special algorithm called the "upwind" finite element method.