Briffa, Keith R.; Osborn, Timothy J.; Schweingruber, Fritz H.; Harris, Ian C.; Jones, Philip D. Journal of Geophysical Research, 106, D3, 2001, pàg. 2929–2941. Bibcode: 2001JGR...106.2929B. DOI: 10.1029/2000JD900617.
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Moschandreas, Maria (2000). Business Economics, 2nd Edition, Thompson Learning, Description and chapter-preview links.
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Briffa, Keith R.; Osborn, Timothy J.; Schweingruber, Fritz H.; Harris, Ian C.; Jones, Philip D. Journal of Geophysical Research, 106, D3, 2001, pàg. 2929–2941. Bibcode: 2001JGR...106.2929B. DOI: 10.1029/2000JD900617.