Citing this Article
 

Owing to the fact that a Living Reviews article may evolve over time, we recommend to cite the article as follows:

Neal Jackson ,
"The Hubble Constant",
Living Rev. Relativity 10,  (2007),  4. URL (cited on <date>):
http://www.livingreviews.org/lrr-2007-4

The date given as <date> then uniquely identifies the version of the article
you are referring to.