The precise value of the Hubble constant, Ho, is today a matter of considerable controversy. The well-known stuay by Sandage and Tammann is published in a series of papers in the Astrophysical Journal from 1974 to 1976. Briefly, Sandage and Tammann determine distances to nearby galaxies in which cepheid variables can be observed. In thoee galaxies, of presumably known distance, they measure the linear diameters of the largest HII regions (which they find to be correlated with galaxy luminosity class). Using these data as calibration, they find distances, and hence absolute magnitudes, of more distant spirals of various luminosity classes from the angular sizes of their largest HII regions, thereby providing a new calibration of the luminosity-class-absolute magnitude relation for Sc spirals. Finally, they use the new calibration to determine distances to still more remote Sc spirals of recognized luminosity class, and whose radial velocities are presumed to be great enough to be indicative of the cosmological Hubble flow. Prom various treatments of their data, they find values for Ho in the range 50 to 55 km s1 Mpc1.