Editing Loran-C (section)

===LORAN chains (GRIs)===
[[File:LORAN Station Malone-Outside-Large.jpg|thumb|right|LORAN Station Malone, [[Malone, Florida]] Great Lakes chain (GRI 8970)/Southeast U.S. chain (GRI 7980)]]
Every LORAN chain in the world uses a unique Group Repetition Interval, the number of which, when multiplied by ten, gives how many microseconds pass between pulses from a given station in the chain. In practice, the delays in many, but not all, chains are multiples of 100 microseconds. LORAN chains are often referred to by this designation, ''e.g.'', GRI 9960, the designation for the LORAN chain serving the [[Northeastern United States]].{{Citation needed|date=May 2009}}

Due to the nature of hyperbolic curves, a particular combination of a primary and two secondary stations can possibly result in a "grid" where the grid lines intersect at shallow angles. For ideal positional accuracy, it is desirable to operate on a navigational grid where the grid lines are closer to right angles ([[Orthogonality|orthogonal]]) to each other. As the receiver travels through a chain, a certain selection of secondaries whose TD lines initially formed a near-orthogonal grid can become a grid that is significantly skewed. As a result, the selection of one or both secondaries should be changed so that the TD lines of the new combination are closer to right angles.<ref>{{Cite book| author=Hefley, Gifford| title=The Development of Loran-C Navigation and Timing (NBS Monograph 129) |year=1972 | publisher=US Dept of Commerce National Bureau of Standards| pages=12 | lccn=72-600267 }}</ref> In practice, nearly all chains provide at least three, and as many as five, secondaries.<ref>{{Cite book| title=AC 90-92 Guidelines for the Operational Use of Loran-C Navigation System Outside of the US National Airspace System (NAS) | year=1993 | publisher=US Dept of Transportation FAA| pages=2 | edition=2012 cancelled}}</ref>