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COMPASS

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{{otheruses}} Image:Compass in a wooden frame.jpg thumb|Compass in a wooden box A '''compass''' (or '''mariner's compass''') is a navigational instrument for finding directions on the earth. It consists of a magnetised pointer free to align itself accurately with Earth's magnetic field Earth's magnetic field direction which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a clock and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. A ''compass'' can be any magnetic device using a needle to indicate the direction of the magnetic north of a planet's magnetosphere. Any instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A '''compass dial''' is a small pocket compass with a sundial. A '''variation compass''' is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass can also be used to ascertain True north.

History of the navigational compass
The compass was invented by Chinese scientists thousands of years ago. The earliest recorded use of lodestone as a direction finder was in a 4th century Chinese book: ''Book of the Devil Valley Master''. ''Dream Pool Essay'' written by Song Dynasty scholar Shen Kua in AD 1086 contained a detailed description of how geomancers magnetized a needle by rubbing its tip with lodestone, and hung the magnetic needle with one single strain of silk with a bit of wax attached to the center of the needle. Shen Kua pointed out that a needle prepared this way sometimes pointed south, sometimes north. The earliest recorded use of a compass in navigation lies in Zhu Yu's book ''Pingzhou Ke Tan'' (Pingzhou Table Talks) of AD 1117. :''The navigator knows the geography, he watches the stars at night, watches the sun at day; when it is dark and cloudy, he watches the compass'' A pilot's compass handbook titled Shun Feng Xiang Song (Fair Winds for Escort) in the Oxford Bodleian Library contains great details about the use of compass in navigation. Eventually, compasses were also used in feng shui in ancient China. They helped feng shui practitioners locate directions because directions are important in the practice of feng shui. For example, in feng shui a south-facing door is considered desirable and harmonious. image:Compass thumbnail.jpg sailor thumb|Navigational [[sailor|mariner's compass.html" title="Meaning of mariner.html" title="Meaning of thumb|Navigational [[sailor|mariner">thumb|Navigational [[sailor|mariner's compass">mariner.html" title="Meaning of thumb|Navigational [[sailor|mariner">thumb|Navigational [[sailor|mariner's compass After this point there is much debate on what happened to compass. Theories include its travel to the Middle East via the Silk Road, and then to Europe, direct transfer of the compass from China the Europe and then later from Europe to the Middle East, as well as independent creation of the compass in Europe and then its transfer thereafter to the Middle East. The latter 2 are supported by evidence of the Arabic word for "Compass" (''al-konbas'') possibly being a derivation of the old Italian word for compass. Other evidence for this includes the earlier mentioning of the compass in European works rather than Arabic. The first European mention of the directional compass occurs in Alexander Neckam's De naturis rerum (On the Natures of Things), probably written in Paris in 1190. As for the Arab world, [http://www.uib.no/jais/v001ht/schmidl1.htm Yemeni Sultan al-Ashraf] appears to be the earliest confimed mention of the compass in 1290, though some authors assert an earlier recording, as early as 1242 for Arabic, and 1231 or Persian. Prior to the introduction of the compass, wayfinding at sea was primarily done via celestial navigation, supplemented in some places by the use of soundings. Difficulties arose where the sea was too deep for soundings and conditions were continually overcast or foggy. Thus the compass was not of the same utility everywhere. For example, the Arabs could generally rely on clear skies in navigating the Persian Gulf and the Indian Ocean (as well as the predictable nature of the monsoons). This may explain in part their relatively late adoption of the compass. Mariners in the relatively shallow Baltic Sea Baltic made extensive use of soundings. In the Mediterranean, however, the practice from ancient times had been to curtail sea travel between October and April, due in part to the lack of dependable clear skies during the Mediterranean winter (and much of the sea is too deep for soundings). With improvements in dead reckoning methods, and the development of better charts, this changed during the second half of the 13th century. By around 1290 the sailing season could start in late January or February, and end in December. The additional few months were of considerable economic importance; it enabled Venice Venetian convoys, for instance, to make two round trips a year to the eastern Mediterranean, instead of one. Around the time Europeans learned of the compass, traffic between the Mediterranean and northern Europe increased, and one factor may be that the compass made traversal of the Bay of Biscay safer and easier.

Construction of a simple compass
Image:Compass_Fitted_To_A_Yacht.jpg yacht.html" title="Meaning of thumb thumb|right|A simple compass typical to a small [[yacht.html" title="Meaning of right|A simple compass typical to a small [[yacht">thumb|right|A simple compass typical to a small [[yacht">right|A simple compass typical to a small [[yacht">thumb|right|A simple compass typical to a small [[yacht A magnetic rod is required when constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way, often by being painted red. Flavio Gioja (fl. 1302), an Italian pilot (harbour) marine pilot, is sometimes credited with perfecting the sailor's compass by suspending its needle over a fleur-de-lis design, which pointed north. He also enclosed the needle in a little box with a glass cover.

Modern navigational compasses
image:liquid filled compass.jpg thumb|Liquid filled compass Image:Silva_Sighting_Compass.jpg thumb Modern navigational compasses hold a magnetized needle inside a fluid-filled capsule; the fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north. Other features common on modern handheld compasses are a baseplate with rulings for measuring distances on maps, a rotating bezel for measuring bearings of distant objects, and a sighting mirror that lets the user see both the compass needle and a distant object at the same time. Further, some modern compasses include an inclinometer for measuring gradients and are adjustable to account for varying Magnetic declination. Mariner's compasses can have two or more magnetic needles permanently attached to a compass card. These move freely on a pivot. A ''lubber line'', which can be a marking on the compass bowl or a small fixed needle indicates the ships heading on the compass card. Traditionally the card is divided into thirty-two points (known as ''rhumb''s), although modern compasses are marked in degrees rather than cardinal points. The glass-covered box (or bowl) contains a suspended gimbal within a binnacle. This preserves the horizontal position. Large ships typically rely on a gyrocompass rather than a magnetic compass for navigation, and increasingly electronic fluxgate compasses are used on smaller vessels. Compasses are available marked in Angular_mil mils - a unit of measurement commonly used by the military.

Solid state compasses
Small compasses found in clocks and other electronic gear are Solid-state electronics usually built out of two or three magnetic field sensors that provide data for a microprocessor. Using Trigonometry the correct heading relative to the compass is calculated. Often, the device is a discrete component which outputs either a digital or analog signal proportional to its orientation. This signal is interpreted by a controller or microprocessor and used either internally, or sent to a display unit. An [http://www.robotics.com/arobot/compass.html example implementation], including parts list and circuit schematics, shows one design of such electronics. The sensor uses ''precision magnetics'' and highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field. The electrical signal is then processed or Digital_electronics digitized.

Compass correction
{{main|Magnetic deviation}} Image:MuseeMarine-compas-p1000468.jpg ferromagnetism thumb|Ship's compass, with the two iron balls which correct the effects of non-[[ferromagnetism|ferromagnetic materials.html" title="Meaning of ferromagnetic.html" title="Meaning of thumb|Ship's compass, with the two iron balls which correct the effects of non-[[ferromagnetism|ferromagnetic">thumb|Ship's compass, with the two iron balls which correct the effects of non-[[ferromagnetism|ferromagnetic materials">ferromagnetic.html" title="Meaning of thumb|Ship's compass, with the two iron balls which correct the effects of non-[[ferromagnetism|ferromagnetic">thumb|Ship's compass, with the two iron balls which correct the effects of non-[[ferromagnetism|ferromagnetic materials A ship's compass must be corrected for errors, called compass deviation, caused by iron and steel in its structure and equipment. The ship is ''swung'', that is rotated about a fixed point while its heading is noted by alignment with fixed points on the shore. A compass deviation card is prepared so that the navigator can convert between compass and magnetic headings. The compass can be corrected in three ways. First the lubber line can be adjusted so that it is aligned with the direction in which the ship travels, then the effects of permanent magnets can be corrected for by small magnets fitted within the case of the compass. The effect of non-ferromagnetism ferromagnetic materials can be corrected by two iron balls mounted on either side of the compass binacle. The graph of the compass deviation can be understood using Fourier series. The coefficient

a_0

representing the error in the lubber line, while

a_1,b_1

the ferromagnetic effects and

a_2,b_2

the non-ferromagnetic component. Fluxgate compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading.

Points of the compass
{{main|Boxing the compass}} The mariner's compass card is divided into thirty-two equally spaced points. Four of these - east, west, north, and south - are the cardinal points, and the names of the others are derived from these.

See also
*Azimuth *Beam compass *coordinates *fluxgate compass *gyrocompass *Gyrosin compass *gyrostatic compass *inertial navigation system *pelorus (instrument) pelorus *radio compass *radio direction finder

External links, resources, and references

- USGS Geomagnetism Program * Amir Aczel, ''The Riddle of the Compass: The Invention that Changed the World'', ISBN 0156007533 * Joseph Needham, Colin A. Ronan: The Shorter Science & Civilisation in China Vol 3 Chapter 1 Magnetism and Electricity. * Science Friday, "''[http://www.sciencefriday.com/pages/2002/May/hour2_053102.html The Riddle of the Compass]''" (interview with Amir Aczel, first broadcast on NPR on May 31, 2002). * Paul J. Gans, [http://scholar.chem.nyu.edu/tekpages/compass.html The Medieval Technology Pages: Compass] * Frederic Lane, "The Economic Meaning of the Invention of the Compass", ''American Historial Review'', vol. 68, pp. 605-617 (1963) * www.howstuffworks.com "''[http://science.howstuffworks.com/compass.htm How compasses work]''" * The Tides By Sir William Thomson (Lord Kelvin) * Evening Lecture To The British Association At The Southampton Meeting on Friday, August 25, 1882 [http://zapatopi.net/kelvin/papers/the_tides.html]. Refers to compas correction by Fourier series. * Admiralty manual of navigation, Chapter XXV The Magnetic Compass (continued) the analysis and correction of the deviation, His Majesty's Stationary Office, London, 1914. * Arrick Robots. Robotics.com Example implementation for digital solid-state compass. ''[http://www.robotics.com/arobot/compass.html ARobot Digital Compass App Note]'' * Williams, J.E.D. ''From Sails to Satellites''. New York: Oxford University Press, 1992. * Frances and Joseph Gies, Cathedral, Forge, and Waterwheel subtitled "Technology and Invention in the Middle Ages". * Petra G. Schmidl ''[http://www.uib.no/jais/v001ht/schmidl1.htm Two Early Arabic Sources on the Magnetic Compass]''
- Compass Tutorial - navigation by compass and map {{Commons|Compass}} Category:Navigational equipment Category:Hiking equipment Category:Orientation Category:Measuring instruments ar:Ø¨ÙˆØµÙ„Ø© br:Nadoz-vor bg:ÐšÐ¾Ð¼Ð¿Ð°Ñ? ca:BrÃºixola cs:Kompas da:Kompas de:Kompass es:BrÃºjula fr:Boussole gl:CompÃ¡s ko:ë‚˜ì¹¨ë°˜ id:Kompas it:Bussola he:×ž×¦×¤×Ÿ la:Pyxis nautica lt:Kompasas nl:Kompas ja:æ–¹ä½?ç£?é‡? no:Kompass pl:Kompas magnetyczny pt:BÃºssola ru:ÐšÐ¾Ð¼Ð¿Ð°Ñ? sq:Busula simple:Compass sl:Kompas fi:Kompassi sv:Kompass th:à¹€à¸‚à¹‡à¸¡à¸—à¸´à¸¨ uk:ÐšÐ¾Ð¼Ð¿Ð°Ñ? zh:æŒ‡å?—é’ˆ '''COMPASS''' is an acronym for '''''COMP''rehensive ''ASS''embler'''. COMPASS is a macro assembly language on Control Data Corporation's CDC 3000 3000 series, CDC 6400 6400 series, CDC 7600 7600 and CDC Cyber Cyber 7 series mainframe computers. There are two ''flavors'' of COMPASS: * COMPASS CP is the assembly language for the CP (Central Processor), the processor running user programs. See CDC_6600#The_Central_Processor_.28CP.29 CDC 6600 CP architecture. * COMPASS PP is the assembly language for the PP (Peripheral Processor), only running operating system code. See CDC_6600#Peripheral_Processors_.28PPs.29 CDC 6600 PP architecture. COMPASS is a classical two-pass assembler with macro and conditional assembly features, and generates a full listing showing both the source assembly code and the generated machine code (in octal). CDC's operating systems were written almost entirely in COMPASS assembly language. Central processor (CP or CPU) hardware maintains 24 operational Processor_register registers; namely A0 to A7, X0 to X7 and B0 to B7. Registers X0 to X7 are 60 bits long and are used to hold data, while registers B0 to B17 are 18 bits long and their major purpose is to hold either memory address addresses or be used as Index register indexing registers, with the exception of B0 that is hardwarewise set to zero. Often as a programming convention, B1 (or B7) contains positive 1. A or Memory address register address registers are also 18 bits long and they have a special way of use in the sense that they form pairs with their corresponding X registers, except A0 that is independent of X0 and vice versa. Whenever an address is set into any of A1 to A5 registers, the data at that memory location (address) is transferred to the corresponding X register, while an address set into one of A6 or A7 registers has the effect of storing the data hold by the corresponding X6 or X7 register to that memory location. However A0 can be used to hold any address without affecting the contents of register X0. CP instruction (computer science) instructions are written in a particularly user-friendly form: "SA1 A0+B1" denotes ''set address register A1 to the sum of address register A0 and index register B1''. This initiates a read from central memory address A1 as explained above. Peripheral processor (PP or PPU) instructions are competely different than CPU instructions. Peripheral processor hardware is simpler; it has an 18-bit A register, a 12-bit Program Address register, a 12-bit Q register and a 22-bit R register (used to accomplish address relocation during central memory read and write instructions). No special job validation is required to assemble peripheral processor programs, but to be executed, such programs require system origin privileges.

Example code
This COMPASS/Sample_Code COMPASS sample code displays the calendar of the year given as a parameter on the Computer_terminal terminal. If no parameter is given, then the calendar of the current year is displayed.

External links

- Scanned COMPASS manuals
- A newer (1986) version of scanned COMPASS manual Category:CDC software {{compu-lang-stub}}

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