No products in the cart. How to Use a Lensatic Compass Posted on October 25, There are so many different kinds of compasses, it can be hard to keep up. Navigation has taken on many forms over the years. Here at Brunton, we manufacture a variety of different compasses for varying needs in the field. A lensatic compass is just one of the many navigational tools we have built.
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Magnetic compass A military compass that was used during World War I The magnetic compass is the most familiar compass type. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation. In navigation, directions on maps are usually expressed with reference to geographical or true north , the direction toward the Geographical North Pole , the rotation axis of the Earth.
Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north , called magnetic declination can vary widely with geographic location. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The effect of this means a map with the latest declination information should be used. Non-magnetic compasses There are other ways to find north than the use of magnetism, and from a navigational point of view a total of seven possible ways exist  where magnetism is one of the seven.
Two sensors that utilize two of the remaining six principles are often also called compasses, i. Gyrocompass Main article: Gyrocompass A gyrocompass is similar to a gyroscope. It is a non-magnetic compass that finds true north by using an electrically powered fast-spinning wheel and friction forces in order to exploit the rotation of the Earth.
Gyrocompasses are widely used on ships. They have two main advantages over magnetic compasses: they find true north, i. No compass is affected by nonferromagnetic metal, although a magnetic compass will be affected by any kind of wires with electric current passing through them. Large ships typically rely on a gyrocompass, using the magnetic compass only as a backup. Increasingly, electronic fluxgate compasses are used on smaller vessels. However, magnetic compasses are still widely in use as they can be small, use simple reliable technology, are comparatively cheap, are often easier to use than GPS , require no energy supply, and unlike GPS, are not affected by objects, e.
GPS receivers used as compasses GPS receivers using two or more antennae mounted separately and blending the data with an inertial motion unit IMU can now achieve 0. The devices accurately determine the positions latitudes, longitudes and altitude of the antennae on the Earth, from which the cardinal directions can be calculated.
Manufactured primarily for maritime and aviation applications, they can also detect pitch and roll of ships. Small, portable GPS receivers with only a single antenna can also determine directions if they are being moved, even if only at walking pace. By accurately determining its position on the Earth at times a few seconds apart, the device can calculate its speed and the true bearing relative to true north of its direction of motion.
Frequently, it is preferable to measure the direction in which a vehicle is actually moving, rather than its heading, i. These directions may be different if there is a crosswind or tidal current. GPS compasses share the main advantages of gyrocompasses.
Additionally, compared with gyrocompasses, they are much cheaper, they work better in polar regions, they are less prone to be affected by mechanical vibration, and they can be initialized far more quickly. However, they depend on the functioning of, and communication with, the GPS satellites, which might be disrupted by an electronic attack or by the effects of a severe solar storm.
Gyrocompasses remain in use for military purposes especially in submarines, where magnetic and GPS compasses are useless , but have been largely superseded by GPS compasses, with magnetic backups, in civilian contexts. History Main article: History of the compass The first compasses in ancient Han dynasty China were made of lodestone , a naturally magnetized ore of iron.
Dry compasses began to appear around in Medieval Europe and the Islamic world. Key points on the compass, including the north end of the needle are often marked with phosphorescent , photoluminescent , or self-luminous materials  to enable the compass to be read at night or in poor light. As the compass fill liquid is noncompressible under pressure, many ordinary liquid-filled compasses will operate accurately underwater to considerable depths.
Many modern compasses incorporate a baseplate and protractor tool, and are referred to variously as " orienteering ", "baseplate", "map compass" or "protractor" designs.
This type of compass uses a separate magnetized needle inside a rotating capsule, an orienting "box" or gate for aligning the needle with magnetic north, a transparent base containing map orienting lines, and a bezel outer dial marked in degrees or other units of angular measurement. A magnetic card compass is usually equipped with an optical, lensatic, or prismatic sight, which allows the user to read the bearing or azimuth off the compass card while simultaneously aligning the compass with the objective see photo.
Magnetic card compass designs normally require a separate protractor tool in order to take bearings directly from a map. M military lensatic compass does not use a liquid-filled capsule as a damping mechanism, but rather electromagnetic induction to control oscillation of its magnetized card.
A "deep-well" design is used to allow the compass to be used globally with a card tilt of up to 8 degrees without impairing accuracy.
The use of air-filled induction compasses has declined over the years, as they may become inoperative or inaccurate in freezing temperatures or extremely humid environments due to condensation or water ingress.
M Cammenga 3H military lensatic compass, the Silva 4b Militaire , and the Suunto M-5N T contain the radioactive material tritium 3 1H and a combination of phosphors. M equipped with self-luminous lighting contains mCi millicuries of tritium. The purpose of the tritium and phosphors is to provide illumination for the compass, via radioluminescent tritium illumination , which does not require the compass to be "recharged" by sunlight or artificial light. Consequently, the illumination of the display will fade.
Traditionally the card is divided into thirty-two points known as rhumbs , 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. Thumb compass Main article: Thumb compass Thumb compass on left A thumb compass is a type of compass commonly used in orienteering , a sport in which map reading and terrain association are paramount.
Consequently, most thumb compasses have minimal or no degree markings at all, and are normally used only to orient the map to magnetic north. An oversized rectangular needle or north indicator aids visibility. Thumb compasses are also often transparent so that an orienteer can hold a map in the hand with the compass and see the map through the compass. The best models use rare-earth magnets to reduce needle settling time to 1 second or less. Solid state compasses Main article: Magnetometer 3-axis electronic magnetometer AKM by AKM Semiconductor Small compasses found in clocks, mobile phones , and other electronic devices are solid-state microelectromechanical systems MEMS compasses, usually built out of two or three magnetic field sensors that provide data for a microprocessor.
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 either used internally, or sent to a display unit. Specialty compasses A standard Brunton Geo, used commonly by geologists Apart from navigational compasses, other specialty compasses have also been designed to accommodate specific uses.
These include: Qibla compass , which is used by Muslims to show the direction to Mecca for prayers. Optical or prismatic compass , most often used by surveyors, but also by cave explorers, foresters, and geologists. These compasses generally use a liquid-damped capsule  and magnetized floating compass dial with an integral optical sight, often fitted with built-in photoluminescent or battery-powered illumination.
Most of these compasses are designed for heavy-duty use, with high-quality needles and jeweled bearings, and many are fitted for tripod mounting for additional accuracy. They were used for land surveying, particularly with plane tables. As the compass is moved closer to one of the magnetic poles, the magnetic declination, the difference between the direction to geographical north and magnetic north, becomes greater and greater.
At some point close to the magnetic pole the compass will not indicate any particular direction but will begin to drift. Also, the needle starts to point up or down when getting closer to the poles, because of the so-called magnetic inclination. Cheap compasses with bad bearings may get stuck because of this and therefore indicate a wrong direction.
Local environments may contain magnetic mineral deposits and artificial sources such as MRIs , large iron or steel bodies, electrical engines or strong permanent magnets. Any electrically conductive body produces its own magnetic field when it is carrying an electric current. Magnetic compasses are prone to errors in the neighborhood of such bodies. Some compasses include magnets which can be adjusted to compensate for external magnetic fields, making the compass more reliable and accurate.
A compass is also subject to errors when the compass is accelerated or decelerated in an airplane or automobile. Compasses that include compensating magnets are especially prone to these errors, since accelerations tilt the needle, bringing it closer or further from the magnets.
Another error of the mechanical compass is turning error. When one turns from a heading of east or west the compass will lag behind the turn or lead ahead of the turn. Magnetometers, and substitutes such as gyrocompasses, are more stable in such situations. Construction of a magnetic compass Magnetic needle A magnetic rod is required when constructing a compass. However, this method produces only a weak magnet so other methods are preferred.
For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic lodestone. 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. Needle-and-bowl device If a needle is rubbed on a lodestone or other magnet, the needle becomes magnetized.
When it is inserted in a cork or piece of wood, and placed in a bowl of water it becomes a compass. Later, these were divided, in China into 24, and in Europe into 32 equally spaced points around the compass card.
For a table of the thirty-two points, see compass points. In the modern era, the degree system took hold. This system is still in use today for civilian navigators. The degree system spaces equidistant points located clockwise around the compass dial. In the 19th century some European nations adopted the " grad " also called grade or gon system instead, where a right angle is grads to give a circle of grads. Dividing grads into tenths to give a circle of decigrades has also been used in armies.
Most military forces have adopted the French " millieme " system. This is an approximation of a milli-radian per circle , in which the compass dial is spaced into units or "mils" for additional precision when measuring angles, laying artillery, etc. The value to the military is that one angular mil subtends approximately one metre at a distance of one kilometer. Imperial Russia used a system derived by dividing the circumference of a circle into chords of the same length as the radius.
Each of these was divided into spaces, giving a circle of The Soviet Union divided these into tenths to give a circle of units, usually translated as "mils". This system was adopted by the former Warsaw Pact countries e. Soviet Union , East Germany , often counterclockwise see picture of wrist compass. This is still in use in Russia. 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. Other magnetic compasses have a small sliding counterweight installed on the needle itself.
This unit is on display in a museum.
I have half a dozen navigation apps on my phone, so I rarely get lost! But phones have several major weaknesses: battery life and signal reception. A compass. Though such a simple device has been around for about a thousand years, compasses have not lost their utility.
The 9 Best Lensatic Compasses
Magnetic compass A military compass that was used during World War I The magnetic compass is the most familiar compass type. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation. In navigation, directions on maps are usually expressed with reference to geographical or true north , the direction toward the Geographical North Pole , the rotation axis of the Earth. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north , called magnetic declination can vary widely with geographic location. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The effect of this means a map with the latest declination information should be used. Non-magnetic compasses There are other ways to find north than the use of magnetism, and from a navigational point of view a total of seven possible ways exist  where magnetism is one of the seven.
How to Use a Lensatic Compass
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