with the same convention of Fig. 3. The black triangles represent the HIFLUGCS sample with filled symbols referring to those objects in the common luminosity range erg s^-1 that yeld a best fit relation with a slope of B = 3.58 (black, dashed line). The best fit of the distant sample assuming the above slope is represented by the blue, dashed line, and the 1σ error is not shown for clarity.