  In this work we perform the first test of a stellar spectral classification
method (Stock & Stock 1999) by applying it to early type stars. The sample of
stars are the members of the open cluster IC 2391 that have high-resolution
spectra available in the UVES Project of Paranal Observatory. We show that, in
general, absolute magnitudes $M_V$ and intrinsic colors $(B-V)_0$ can be
recovered within the uncertainties stated in the original calibration ($\sim
0.4$ for the magnitudes and $\sim 0.03$ for the colors). This accuracy allows
us to estimate distances and to infer membership of individual stars to obtain
an average distance to the cluster of $156\pm 24$ pc, which is in good
agreement with previous reported determinations. Finally, we identify and
discuss the real strengths and limitations of this method and we suggest how it
can be improved for future studies.
