A brief history of the determination of the Hubble constant H _ { 0 } is given .
Early attempts following Lemaître ( 1927 ) gave much too high values due to errors of the magnitude scale , Malmquist bias and calibration problems .
By 1962 most authors agreed that 75 \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } H% _ { 0 } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } % } 130 .
After 1975 a dichotomy arose with values near 100 and others around 55 .
The former came from apparent-magnitude-limited samples and were affected by Malmquist bias .
New distance indicators were introduced ; they were sometimes claimed to yield high values of H _ { 0 } , but the most recent data lead to H _ { 0 } in the 60 ’ s , yet with remaining difficulties as to the zero-point of the respective distance indicators .
SNe Ia with their large range and very small luminosity dispersion ( avoiding Malmquist bias ) offer a unique opportunity to determine the large-scale value of H _ { 0 } .
Their maximum luminosity can be well calibrated from 10 SNe Ia in local parent galaxies whose Cepheids have been observed with HST .
An unforeseen difficulty – affecting all Cepheid distances – is that their P-L relation varies from galaxy to galaxy , presumably in function of metallicity .
A proposed solution is summarized here .
The conclusion is that H _ { 0 } = 63.2 \pm 1.3 ( random ) \pm 5.3 ( systematic ) on all scales .
The expansion age becomes then ( with \Omega _ { m } = 0.3 , \Omega _ { \Lambda } = 0.7 ) 15.1 Gyr .