The right-hand ordinate shows the ΔE(B − V)-value needed to obtain a constant m_bol,0 = 1.86. Relatively small differences in E(B − V) appear to be needed. The left-hand ordinate displays the “unreddened” bolometric magnitude given as m_bol = V − A_V + BC, with A_V = R × E(B − V), for the timeframe 1942–1996. The mean value of m_bol,0 for 1919–1973 seem to cluster around a value near to m_bol,0 = 1.86, while for 1973–1996 a larger range of values is involved. This forms step 4.