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Stainless Steel Drawing Compass Math Geometry Tools for Circles, Total 5 Pieces (Included Box)

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Other features found on modern orienteering compasses are map and romer scales for measuring distances and plotting positions on maps, luminous markings on the face or bezels, various sighting mechanisms (mirror, prism, etc.) for taking bearings of distant objects with greater precision, gimbal-mounted, "global" needles for use in differing hemispheres, special rare-earth magnets to stabilize compass needles, adjustable declination for obtaining instant true bearings without resorting to arithmetic, and devices such as inclinometers for measuring gradients. [17] The sport of orienteering has also resulted in the development of models with extremely fast-settling and stable needles utilizing rare-earth magnets for optimal use with a topographic map, a land navigation technique known as terrain association. [18] Many marine compasses designed for use on boats with constantly shifting angles use dampening fluids such as isopar M or isopar L to limit the rapid fluctuation and direction of the needle. [19] A magnetic compass points to magnetic north pole, which is approximately 1,000 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 1914. [34] Deviation refers to the response of the compass to local magnetic fields caused by the presence of iron and electric currents; one can partly compensate for these by careful location of the compass and the placement of compensating magnets under the compass itself. 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.

A compass. Not the magnetic kind, but the drawing kind. Any decent stationers will have a wide range to choose from. You need one that will hold your pencil firmly, does not have a loose hinge, and has a point - the "safe" compasses slip too easily. I prefer those compasses that have a knurled knob at the hinge, as they allow for a smooth, one-handed action. The best compasses are adjusted by means of a wheel on a screw-thread near the hinge, because these are least likely to slip. Distances can be measured on a map using compasses with two spikes, also called a dividing compass (or just "dividers"). The hinge is set in such a way that the distance between the spikes on the map represents a certain distance in reality, and by measuring how many times the compasses fit between two points on the map the distance between those points can be calculated.Turning the compass scale on the map (D – the local magnetic declination) When the needle is aligned with and superimposed over the outlined orienting arrow on the bottom of the capsule, the degree figure on the compass ring at the direction-of-travel (DOT) indicator gives the magnetic bearing to the target (mountain). Compasses-and-straightedge constructions are used to illustrate principles of plane geometry. Although a real pair of compasses is used to draft visible illustrations, the ideal compass used in proofs is an abstract creator of perfect circles. The most rigorous definition of this abstract tool is the "collapsing compass"; having drawn a circle from a given point with a given radius, it disappears; it cannot simply be moved to another point and used to draw another circle of equal radius (unlike a real pair of compasses). Euclid showed in his second proposition (Book I of the Elements) that such a collapsing compass could be used to transfer a distance, proving that a collapsing compass could do anything a real compass can do. Kemp, Peter, ed. (1988). "Box the Compass". The Oxford Companion to Ships and the Sea. Oxford University Press. p. 103. ISBN 0-19-282084-2. 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. [35] Soldier using a prismatic compass to get an azimuth If you invest in a compass that does not hold a pencil, but instead holds a small piece of graphite, you will find a small piece of sandpaper useful for maintaining the bevelled point (and far cheaper than dedicated sharpeners).

Among the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since c. 206 BC), [1] [2] and later adopted for navigation by the Song Dynasty Chinese during the 11th century. [3] [4] [5] The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190. [6] [7] 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. [32] The coefficient a 0 {\displaystyle a_{0}} represents the error in the lubber line, while a 1 , b 1 {\displaystyle a_{1},b_{1}} the ferromagnetic effects and a 2 , b 2 {\displaystyle a_{2},b_{2}} the non-ferromagnetic component. [33] Navigation texts dating from the Yuan, Ming, and Qing dynasties in China use a 24-pointed compass with named directions. These are based on the twelve Earthly Branches, which also form the basis of the Chinese zodiac. When a single direction is specified, it may be prefaced by the character 單 (meaning single) or 丹.Kreutz, Barbara M. (1973). "Mediterranean Contributions to the Medieval Mariner's Compass". Technology and Culture. 14 (3): 367–383. doi: 10.2307/3102323. JSTOR 3102323. S2CID 111540460. Boardman, David (1983). Graphicacy and Geography Teaching. p.41. In particular they should learn that wind direction is always stated as the direction from which, and not to which, the wind is blowing. Once children have grasped these eight points they can learn the full sixteen points of the compass. The handle, a small knurled rod above the hinge, is usually about half an inch long. Users can grip it between their pointer finger and thumb. E. Chambers Cyclopaedia: or, an Universal Dictionary of Arts and Science, 5th Ed, 1743, pp.206–7, "Points of the Compass, or Horizon, &c., in Geography and Navigation, are the points of division when the whole circle, quite around, is divided into 32 equal parts. These points are therefore at the distance of the 32 d part of the circuit, or 11°15′, from each other; hence 5° 37 + 1 / 2′ is the distance of the half points and 2° 48 + 3 / 4′ is the distance of the quarter points. The needle point is located on the steady leg, and serves as the center point of the circle that is about to be drawn.

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