In this conference, R. Triay has demonstrated the importance to define a statistical model describing the Tully-Fisher (TF) relation in the M-p plane. As long as the same model is used during the calibration step and the step of the determination of the distances of galaxies, standard statistical methods such as the maximum likelihood technic permits us to derive bias free estimators of the distances of galaxies. However in practice, it is convenient to use a different statistical model for calibrating the TF relation (because of its robustness, the Inverse TF (ITF) relation is prefered during this step) and for determinating the distances of galaxies (the Direct TF (DTF) relation is more accurate and robust in this case). So, is it possible to infer the calibration parameters of the DTF relation needed to determinate the distances of galaxies from the calibration parameters of the ITF relation obtained during the calibration step ?. Assuming standard working hypothesis, we prove in Rauzy&Triay (1996) that the ITF and DTF models are in fact mathematically equivalent (i.e. they describe the same physical data distibution in the TF diagram). Thus, it turns out that as long as the calibration parameters are obtained for a given model, we can deduce the corresponding parameters of the other model. Herein, we present this formulas of correspondance. In practice, the best suitable model will be choosen with regard to the selection effects in observation affecting the analysed sample during each of this 2 steps.