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Line 5: − A gyrocompass, also known as a ''direction indicator'', is another instrument designed to indicate north. They are mainly used in aircraft, where the change in atttude of an aircraft can affect the direction of a normal magnetic compass. The principle of a gyrocompass relies upon a rapidly spinning wheel (usually run electrically) which maintains its original orientation. Due to the [[law of conservation of angular momentum]], a gyrocompass can be set to point to true north when it is initialized, and it will continue to point to true north. Gyrocompasses will drift over time, and therefore need to be resynchronized with a magnetic compass at regular intervals.+ − Magnetic compasses were in early use by [[Portugal|Portuguese]] explorers in the [[Age of Exploration]].+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + − + + +
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Deviation from true north can also occur due to the presence of nearby large metal objects, such as ships at sea. At sea, this additional magnetic deviation is tracked, logged, and factored in to reading a magnetic compass in order to determine true north. In an aircraft the aircraft's movement can affect a compass, causing it to give inaccurate readings during turns and other maneuvers.
Deviation from true north can also occur due to the presence of nearby large metal objects, such as ships at sea. At sea, this additional magnetic deviation is tracked, logged, and factored in to reading a magnetic compass in order to determine true north. In an aircraft the aircraft's movement can affect a compass, causing it to give inaccurate readings during turns and other maneuvers.
Magnetic compasses were first invented as a device for [[divination]] as early as the [[Chinese]] [[Han Dynasty]] (since about 206 BC).<ref>{{cite book|last=Merrill|first=Ronald T.|title=The Earth's magnetic field: Its history, origin and planetary perspective|year=1983|publisher=Academic press|location=San Francisco|isbn=0-12-491242-7|page=1|edition=2nd printing|author2=McElhinny, Michael W.}}</ref> Magnetic compasses were in early use by [[Portugal|Portuguese]] explorers in the [[Age of Exploration]].
Compasses are one of the two most essential pieces of navigation gear that one should carry, the other being a [[map]]. [[GPS]] devices and [[cell phone]]s with [[Google]] Maps may breakdown or run out of [[battery|batteries]] during an [[emergency]], [[disaster]] or a [[Post Apocalyptic World]] - [[SHTF]] - [[TEOTWAWKI]] event. Also the sun isn't always shining, and it takes a great deal of time and effort to learn to stellar navigation, however a map and compass will continue to work until your break or lose them.
Few things are more important than knowing where you are and where you're going and the compass helps you to do both. In selecting a compass there many types with many different features to consider, some of them are novelties while others are tremendous conveniences. There are several basic types of compass, and some compasses fall under more than one type.
==Types of Compass==
===Button Compass===
Button compasses are very small offering a decent idea of which was is north and not much more. They are generally part of one's [[Every Day Carry|EDC]], being attached to a keychain or are of a very small [[:Category:Survivalism|survival]] kit.
===Gyrocompass===
A gyrocompass, also known as a ''direction indicator'', is another instrument designed to indicate north. They are mainly used in aircraft, where the change in altitude of an aircraft can affect the direction of a normal magnetic compass. The principle of a gyrocompass relies upon a rapidly spinning wheel (usually run electrically) which maintains its original orientation. Due to the [[law of conservation of angular momentum]], a gyrocompass can be set to point to true north when it is initialized, and it will continue to point to true north. Gyrocompasses will drift over time, and therefore need to be resynchronized with a magnetic compass at regular intervals.
===Baseplate Compass===
Baseplate compass are generally clear with various markings on them, they are designed to be easier to navigate with a map. They are often very feature rich and come at a variety of price points.
===Sighting Compass===
Sighting Compasses generally have either a mirror or sighting whole on perpendicular folding part of the compass. They allow you to look at both the compass and a landmark and line them up for better navigation.
===Transit===
The Transit is the "grand daddy" of compasses, usually including many features, however these are more of a miner or engineer's tool. They are extremely expensive, but offer many abilities other compasses do not.
==Compass Features==
===Declination Scale===
Magnetic North is not in the same location as true North and depending on where you are in the world the difference between a magnetic North reading and where truth North is could vary by a couple of degrees or 30. A Declination scale allows you to calculate or adjust for this difference by knowing approximately where you are in the world and what the deviation is. If you have a fixed declination scale you will have to do the math, but if you have an adjustable deviation scale you can set it and forget it until you are in a location far away.
===Floating===
A compass that floats could be a life saver in some situations.
===Lanyard Attachment===
A [[lanyard]] attachment is a common and highly recommended feature, this will help you to avoid losing your compass.
===Luminescent Points===
If you have to navigate at night, glow in the dark compass point will be extremely helpful.
==See Also==
* [[Map]] and Compass
* [[Orienteering]]
* [[Geocaching]]
* [[GPS]]
* [[Survivalist retreat|Bugout via Map]]
* [[:Category:Survivalism|Survivalism]]
==References==
{{Reflist|2}}
==Bibliography==
* Admiralty, Great Britain (1915) ''Admiralty manual of navigation, 1914'', Chapter XXV: "The Magnetic Compass (continued): the analysis and correction of the deviation", London : HMSO, 525 p.
* Lane, Frederic C. (1963) "The Economic Meaning of the Invention of the Compass", ''The American Historical Review'', '''68''' (3: April), p. 605–617
* Gurney, Alan (2004) ''Compass: A Story of Exploration and Innovation'', London : Norton, ISBN 0-393-32713-2
* Johnson, G. Mark, ''The Ultimate Desert Handbook'', 1st Ed., Camden, Maine: McGraw-Hill (2003), ISBN 0-07-139303-X
* David Buisseret, ed., ''Monarchs, Ministers and Maps: The Emergence of Cartography as a Tool of Government in Early Modern Europe.'' Chicago: University of Chicago Press, 1992, ISBN 0-226-07987-2
* ''The Complete Idiot's Guide to Geocaching'' by Jack W. Peters (ISBN 1-59257-235-9)
* ''Geocaching For Dummies'' by Joel McNamara (ISBN 978-0-7645-7571-6)
==External Links==
* [http://msi.nga.mil/MSISiteContent/StaticFiles/HoMCA.pdf]Handbook of Magnetic Compass Adjustment.
* [http://www.magnet.fsu.edu/mediacenter/slideshows/compass/index.html How to Make a Compass] Audio slideshow from the National High Magnetic Field Laboratory
* Paul J. Gans, [http://scholar.chem.nyu.edu/tekpages/compass.html The Medieval Technology Pages: Compass]
* [http://thegearjunkie.com/the-thumb-compass The Gear Junkie] - review of two orienteering thumb compasses
* [http://www.compassmuseum.com/ COMPASSIPEDIA, the great virtual Compass Museum] gives comprehensive information about all sorts of compasses and how to use them.
* [http://geographyfieldwork.com/UsingCompass.htm Geography fieldwork]
* [http://www.orienteering.org/ International Orienteering Federation]
* [http://www.geocaching.com/ www.geocaching.com]
* [http://www.youtube.com/watch?v=v58-RqssqUc YouTube.com: Orienteering, USOF style]
* https://www.amazon.com/Suunto-Arrow-6-Orienteering-Compass/dp/B003JYVMJC
[[Category:Inventions]]
[[Category:Navigation]]
[[Category:Navigation]]
[[Category:Inventions]]
[[Category:Geography]]
[[Category:Survivalism]]
[[Category:Travel]]