Sandage, A.; Tammann, G. A. (December 1974). "Steps toward the Hubble constant. IV - Distances to 39 galaxies in the general field leading to a calibration of the galaxy luminosity classes and a first hint of the value of H sub 0". The Astrophysical Journal. 194: 559. Bibcode:1974ApJ...194..559S. doi:10.1086/153275. ISSN0004-637X.
Sandage, A.; Tammann, G. A. (December 1974). "Steps toward the Hubble constant. IV - Distances to 39 galaxies in the general field leading to a calibration of the galaxy luminosity classes and a first hint of the value of H sub 0". The Astrophysical Journal. 194: 559. Bibcode:1974ApJ...194..559S. doi:10.1086/153275. ISSN0004-637X.
Sandage, A.; Tammann, G. A. (December 1974). "Steps toward the Hubble constant. IV - Distances to 39 galaxies in the general field leading to a calibration of the galaxy luminosity classes and a first hint of the value of H sub 0". The Astrophysical Journal. 194: 559. Bibcode:1974ApJ...194..559S. doi:10.1086/153275. ISSN0004-637X.