Historical Values of Ho

As you can see, estimates of the current Hubble parameter, Ho have changed dramatically since Hubble's original estimate near 550 km/s/Mpc. The greatest change came in 1952 when Walter Baade recognised the difference between Pop-I and Pop-II Cepheid variables, and the distance scale changed by a factor of two "overnight". You can also see the tendency in the 1980s for there to be two consistently different values -- the "low" value near 50 (Sandage et al), and the high value near 100 (de Vaucouleurs et al).

Figure from OU text "Galaxies and Cosmology"