^Giles, Jim (2001 Apr 19). "EU plans global positioning system". Nature. 410 ((6831)): 853. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); More than one of |pages= and |page= specified (help)
^Foster, James (Jun 14, 2012). "Ship GPS could flag tsunamis". Nature. 486 ((7402)): 161. {{cite journal}}: |access-date= requires |url= (help); More than one of |pages= and |page= specified (help)
^Tsui, James Bao-Yen. (2000). Fundamentals of global positioning system receivers : a software approach. New York [etc.] : John Wiley & Sons. p. 238. {{cite book}}: |access-date= requires |url= (help)
^Johnson, Kevin (Feb 7, 2012). "FBI using GPS surveillance less often following high court ruling.(NEWS)(Global Positioning System)". USA Today: 05A. {{cite journal}}: |access-date= requires |url= (help)
