The coefficients A, B, c and D are obtained empirically. Later, this model was used as one of the assumptions of Mayr. This formula is valid only for a current interval of a hundred of Amperes. The limitations of this model are rapidly reached because it does not take into account the criterion indicating the temporal character of the voltage and current variations. Used in a circuit, it does not explain temporaly how the discharge is stabilized to reach the polarisation point. Later, this model was used as one of the assumptions of Mayr. Mayr reduced the model to the hyperbolic form: