BLABBERMOUTH.NET - ROB HALFORD, ROBERT PLANT, BON SCOTT, OZZY Are Among 'Heavy Metal's All-Time Top 100 Vocalists'. web.archive.org [online]. 2011-06-06 [cit. 2022-11-02]. Dostupné v archivu pořízeném z originálu dne 2011-06-06.
web.archive.org
BLABBERMOUTH.NET - ROB HALFORD, ROBERT PLANT, BON SCOTT, OZZY Are Among 'Heavy Metal's All-Time Top 100 Vocalists'. web.archive.org [online]. 2011-06-06 [cit. 2022-11-02]. Dostupné v archivu pořízeném z originálu dne 2011-06-06.