On the derivation of the Tully-Fisher relations

The Hubble constant H0 should not show distancedependence. An inappropriate use of the direct Tully-Fisher relation may lead to a conclusion that H0 is dependent on the distance. This paper tries to answer the question: is it possible to avoid the caveats of the direct relation by applying the inverse Tully-Fisher relation. Under ideal conditions it is possible simultaneously to determine the inverse slope precisely and to find the Hubble constant next to calibration. Ideal conditions are, however, rarely met. Two particular sources of error in the resulting averageHubble constant are considered.A progressive measurement error in angular diameters (apparent magnitudes) causes overestimation of H0. An asymmetry in the logVmaxdistribution in the sense of a tail of small rotational velocities tends to shift H0 upwards.