Sagan, Carl (October 2000) [1973]. Jerome Agel, ed. Cosmic Connection: An Extraterrestrial Perspective. Freeman J. Dyson, David Morrison. Cambridge Press. ISBN0-521-78303-8. Consultado el 4 de noviembre de 2015. «I would suggest Type 1.0 as a civilization using 1016 watts for interstellar communication; Type 1.1, 1017 watts; Type 1.2, 1018 watts, and so on. Our present civilization would be classed as something like Type 0.7.»