* {{cite book |author = David Ewing Duncan |title = The Calendar |year = 1999 |publisher = |pages = 331–332 |isbn = 978-1-85702-979-6 }}
* {{cite book |author = Duncan Steel |title = Marking Time: The Epic Quest to Invent the Perfect Calendar |year = 2000 |publisher = John Wiley and Sons |pages = 149–151 |url = https://books.google.com/books?id=fsni_qV-FJoC&printsec=frontcover&pg=PA149 |isbn = 978-0-471-29827-4 }}
* {{cite book |author = Günther A. Wagner |title = ''Age Determination of Young Rocks and Artifacts: Physical and Chemical Clocks in Quaternary Geology and Archeology'' |year = 1998 |publisher = Springer |url = https://books.google.com/books?id=ADuZDCa08kwC&pg=PA48 |page = 48 |isbn = 978-3-540-63436-2 }}
