Cresson H. Kearny, Nuclear War Survival Skills, Oregon Institute of Science and Medicine, 1987 revised edition. May be freely distributed (see copyright page).
https://github.com/davepinch/pinchy.cc/blob/master/content/topics/works/c/cresson-h-kerney/nuclear-war-survival-skills/online-copy/archive.org.md
The distance to Messier 81 has been measured by Freedman et al to be 3.63 ± 0.34 Megaparsecs (11.8 ± 1.1 million light years) by using the Hubble Space Telescope to identify classical Cepheid variables and measure their periods using the period-luminosity relation discovered by Henrietta Swan Leavitt.