Allan Sandage returned to the distance scale and the calibration of the Hubble constant again and again during his active life , experimenting with different distance indicators .
In 1952 his proof of the high luminosity of Cepheids confirmed Baade ’ s revision of the distance scale ( H _ { 0 } \sim 250 { km s } ^ { -1 } { Mpc } ^ { -1 } ) .
During the next 25 years , he lowered the value to 75 and 55 .
Upon the arrival of the Hubble Space Telescope , he observed Cepheids to calibrate the mean luminosity of nearby Type Ia supernovae ( SNe Ia ) which , used as standard candles , led to the cosmic value of H _ { 0 } = 62.3 \pm 1.3 \pm 5.0 { km s } ^ { -1 } { Mpc } ^ { -1 } .
Eventually he turned to the tip of the red-giant branch ( TRGB ) as a very powerful distance indicator .
A compilation of 176 TRGB distances yielded a mean , very local value of H _ { 0 } = 62.9 \pm 1.6 { km s } ^ { -1 } { Mpc } ^ { -1 } and shed light on the streaming velocities in the Local Supercluster .
Moreover , TRGB distances are now available for six SNe Ia ; if their mean luminosity is applied to distant SNe Ia , one obtains H _ { 0 } = 64.6 \pm 1.6 \pm 2.0 { km s } ^ { -1 } { Mpc } ^ { -1 } .
The weighted mean of the two independent large-scale calibrations yields H _ { 0 } = 64.1 { km s } ^ { -1 } { Mpc } ^ { -1 } within 3.6 % .