Global Positioning System 18 : A system used for locating objects on Earth precisely, using a system of satellites in geostationary orbit in space. Often used by digital relays to obtain accurate time information
Young & Company Electric Power Products and Related Engineering Services, Glossary of Electrical Terms, http://www.youngco.com/young2.asp?ID=4&Type=3, CA., USA 2001. (Electr Sfty - Amer) {514}