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Published online by Cambridge University Press: 30 March 2016
The traditional approach to the extragalactic distance scale has been through several levels of primary, secondary and tertiary indicators of increasing range and decreasing precision. This piecemeal approach, fraught with the danger of cumulative errors, has led in recent years to two widely divergent scales, the “long” scale of Sandage and Tammann (1974–1982), leading to ≃ 50 km s-1 Mpc-1, and the “short” scale of the author (1978–79), leading to Ho ≃ 100 (de Vaucouleurs and Bollinger 1979; de Vaucouleurs and Peters 1981; de Vaucouleurs et al. 1981). The divergence, increasing from ~ 0.4 mag in the Local Group to ~ 1.2 mag at the distance of the Virgo Cluster, indicates that at least one of the scales is not linear (de Vaucouleurs 1981).