Letham, L. (1998). GPS made easy: Using global positioning systems in the outdoors (2nd ed.). Mountaineers.
Chicago-referens (17:e uppl.)Letham, Lawrence. GPS Made Easy: Using Global Positioning Systems in the Outdoors. 2nd ed. Seattle: Mountaineers, 1998.
MLA-referens (9:e uppl.)Letham, Lawrence. GPS Made Easy: Using Global Positioning Systems in the Outdoors. 2nd ed. Mountaineers, 1998.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.