The Compass of the World
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Most manufacturers balance their compass needles for one of five zones, ranging from zone 1, covering most of the Northern Hemisphere , to zone 5 covering Australia and the southern oceans. This individual zone balancing prevents excessive dipping of one end of the needle which can cause the compass card to stick and give false readings. Some compasses feature a special needle balancing system that will accurately indicate magnetic north regardless of the particular magnetic zone.
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Other magnetic compasses have a small sliding counterweight installed on the needle itself. This sliding counterweight, called a 'rider', can be used for counterbalancing the needle against the dip caused by inclination if the compass is taken to a zone with a higher or lower dip. Like any magnetic device, compasses are affected by nearby ferrous materials, as well as by strong local electromagnetic forces.
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Compasses used for wilderness land navigation should not be used in proximity to ferrous metal objects or electromagnetic fields car electrical systems, automobile engines, steel pitons , etc. Large amounts of ferrous metal combined with the on-and-off electrical fields caused by the vehicle's ignition and charging systems generally result in significant compass errors.
At sea, a ship's compass must also be corrected for errors, called 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 ferromagnetic materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binnacle in concert with permanent magnets and a Flinders bar. A similar process is used to calibrate the compass in light general aviation aircraft, with the compass deviation card often mounted permanently just above or below the magnetic compass on the instrument panel.
Fluxgate electronic compasses can be calibrated automatically, and can also be programmed with the correct local compass variation so as to indicate the true heading. A magnetic compass points to magnetic north pole, which is approximately 1, miles from the true geographic North Pole. A magnetic compass's user can determine true North by finding the magnetic north and then correcting for variation and deviation. Variation is defined as the angle between the direction of true geographic north and the direction of the meridian between the magnetic poles.
Variation values for most of the oceans had been calculated and published by Mariners have long known that these measures do not completely cancel deviation; hence, they performed an additional step by measuring the compass bearing of a landmark with a known magnetic bearing. They then pointed their ship to the next compass point and measured again, graphing their results. In this way, correction tables could be created, which would be consulted when compasses were used when traveling in those locations.
Mariners are concerned about very accurate measurements; however, casual users need not be concerned with differences between magnetic and true North. Except in areas of extreme magnetic declination variance 20 degrees or more , this is enough to protect from walking in a substantially different direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired.
By carefully recording distances time or paces and magnetic bearings traveled, one can plot a course and return to one's starting point using the compass alone. Compass navigation in conjunction with a map terrain association requires a different method. To take a map bearing or true bearing a bearing taken in reference to true, not magnetic north to a destination with a protractor compass , the edge of the compass is placed on the map so that it connects the current location with the desired destination some sources recommend physically drawing a line.
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The orienting lines in the base of the compass dial are then rotated to align with actual or true north by aligning them with a marked line of longitude or the vertical margin of the map , ignoring the compass needle entirely. If a magnetic north bearing or compass bearing is desired, the compass must be adjusted by the amount of magnetic declination before using the bearing so that both map and compass are in agreement.
Some compasses allow the scale to be adjusted to compensate for the local magnetic declination; if adjusted correctly, the compass will give the true bearing instead of the magnetic bearing.
The modern hand-held protractor compass always has an additional direction-of-travel DOT arrow or indicator inscribed on the baseplate. To check one's progress along a course or azimuth, or to ensure that the object in view is indeed the destination, a new compass reading may be taken to the target if visible here, the large mountain. After pointing the DOT arrow on the baseplate at the target, the compass is oriented so that the needle is superimposed over the orienting arrow in the capsule.
The resulting bearing indicated is the magnetic bearing to the target. Again, if one is using "true" or map bearings, and the compass does not have preset, pre-adjusted declination, one must additionally add or subtract magnetic declination to convert the magnetic bearing into a true bearing. The exact value of the magnetic declination is place-dependent and varies over time, though declination is frequently given on the map itself or obtainable on-line from various sites.
If the hiker has been following the correct path, the compass' corrected true indicated bearing should closely correspond to the true bearing previously obtained from the map. A compass should be laid down on a level surface so that the needle only rests or hangs on the bearing fused to the compass casing — if used at a tilt, the needle might touch the casing on the compass and not move freely, hence not pointing to the magnetic north accurately, giving a faulty reading. To see if the needle is well leveled, look closely at the needle, and tilt it slightly to see if the needle is swaying side to side freely and the needle is not contacting the casing of the compass.
If the needle tilts to one direction, tilt the compass slightly and gently to the opposing direction until the compass needle is horizontal, lengthwise. Items to avoid around compasses are magnets of any kind and any electronics. Magnetic fields from electronics can easily disrupt the needle, preventing it from aligning with the Earth's magnetic fields, causing inaccurate readings. The Earth's natural magnetic forces are considerably weak, measuring at 0. Exposure to strong magnets, or magnetic interference can sometimes cause the magnetic poles of the compass needle to differ or even reverse.
Avoid iron rich deposits when using a compass, for example, certain rocks which contain magnetic minerals, like Magnetite. This is often indicated by a rock with a surface which is dark and has a metallic luster, not all magnetic mineral bearing rocks have this indication. To see if a rock or an area is causing interference on a compass, get out of the area, and see if the needle on the compass moves. If it does, it means that the area or rock the compass was previously at is causing interference and should be avoided.
From Wikipedia, the free encyclopedia. This article is about the direction finding instrument used in navigation.
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For other uses, see Compass disambiguation. Main article: Gyrocompass. Main article: History of the compass. Main article: Thumb compass. Main article: Magnetometer. Main article: Points of the compass. Main article: Magnetic deviation. Fundamentals of Geophysics. London: Cambridge University Press. Early in the Han Dynasty, between — BC, the Chinese fashioned a rudimentary compass out of lodestone In Ibrahim Kalin ed.
Oxford University Press. Therefore the needle of a compass only approximately points to the magnetic poles. Retrieved The Journal of Navigation. The Earth's magnetic field: Its history, origin and planetary perspective 2nd printing ed. San Francisco: Academic press. Tritium has the advantage that its radiation has such low energy that it cannot penetrate a compass housing.
Mark The Ultimate Desert Handbook. McGraw-Hill Professional. Patent No. December Retrieved 11 February Compass category.
An Overview and History of the Compass
In order to get an accurate reading from a compass, the compass needle needs to be "balanced" in the capsule, so it does not drag on the top or bottom of the capsule. But, because the horizontal and vertical components of the earth's magnetic field vary considerably in different locations, a compass needle that "balances" perfect in North America will drag or stick in South America. As a result of these magnetic variances, the compass industry has divided the earth into 5 "zones", as identified in the map below.
All of the standard compasses sold at The Compass Store are balanced for zone 1 since most of our sales are in North America. China military used a compass for navigational orienteering in the 11th century and for naval orienteering in 12th. Later was invented a turtle the compass, which was a type of dry compass.
Its main part was a wooden turtle which had lodestone in it which was fixed with wax and had a needle sticking out. Wooden turtle balanced on a bamboo needle, which allowed it to rotate freely and the needle pointed north. In the 12th century compass appeared in Europe. Both types of compass appeared: a floating compass for astronomical purposes and a dry compass for seafaring. It improved sailing which, until then, relied on orientation by the sun or by stars and was limited to sea travel between October and April. Now ships could sail throughout the whole year. Islamic world imported compass during the 13th century and used it for the same purposes as the rest of the world: astronomy and seafaring.