Learn how to use the lensatic compass used by the US Military. PRECISION COMPASS. * LENSATIC *. PROVEN • RUGGED ACCURATE. CAMMENGA. FAX ( ANILINE AVE. HOLLAND, MICHIGAN I get lots of questions via email from people wanting to know how to use a lensatic compass, and I think I’ve covered that pretty well in a series of two posts.
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The only problem is that this process takes time and tools.
Lensatic Compass Guide
There’s a better way, I believe, from both a time and an accuracy standpoint. Be sure you understand magnetic declination.
Hold a compass level and steady to prevent the needle from touching the sides of the globe or the dial face. The normal method to transfer manhal from your lensatic compass to your map and back is with a protractor and a pencil. A web source of such a map is given in the References. Take your lensatic compass and open it up all the way so it is one flat line.
That’s the reason for this page, where I’ll tell what I know about the lensatic compass from long acquaintance though not much recent use. Note the red number on the dial, which is the degrees under the black index line on the compass face. There is a ring near the rear sight used for holding the compass; the thumb generally is placed in the ring, and both hands are used, taking care to level the compass.
With a hand-held compass, we cannot set the compass on line, and then look down and note the position of a needle, as with a surveying compass, but must read the bearing simultaneously with the sighting.
Deviation cannot be predicted, and must always be considered when using a compass. Distances cojpass this can be determined from the map, or from a vehicle odometer, if great precision is not required. At that point you know what direction you need to head to get to your next stop, and if you pair that with an negineer distance you’ll be on your way in no time.
That is, take the azimuth you recorded and subtract degrees from it, or mills if using a military lensatic compass. An iron Flinder’s bar is one example. Another useful exercise is locating yourself on a map emgineer taking bearings to two or more visible points and then plotting the back bearings on a map.
Making sure you don’t move to change directions, turn the glass compass housing until the short luminous line is directly lined up with the luminous magnetic arrow. Lenastic it square and straight in front of you like you mean business. Engineed of Interest An “azimuth” is pretty much the same as a “bearing. Calvert Created 1 September Last revised 4 December There are also magnetic anomalies that give strange effects in localized areas.
It seems to use topographic maps and a compass lensattic a flat case with straight edges for use with the map, of which Silva is a popular brand name. The magnetism of ships has been used to detonate underwater mines, by detecting the disturbance of the geomagnetic field.
Open the compass completely and hold it level in front of you. L ook through the sighting slot and find some target a tree, boulder, whatever that lines up with your sighting wire. To check your process, and even add a little more accuracy to it, find another feature and perform the same steps. A web search for “magnetic declination” will find world maps that are quite interesting, showing places where the compass is useless. Depending on which text editor lnsatic pasting into, you might have to add the italics to the site name.
Lensatic Compass Guide
They have no significance for compass measurements, but are of intrinsic interest, and this seems the best place to discuss them. If you don’t happen to be in Northern Colorado, you can construct a similar example any convenient place near you, and do it as a compass or a map exercise. The intersection gives your position.
There’s a lot of room for error and mistakes, and it takes time, which is manuwl a very precious commodity. Keep doing this until you get to where you want to go.
Most people are aware that lensatic compasses are fitted with small amounts of tritium around the dial. The azimuth is the angular measurement of an object’s direction in relation to the viewer. A few terms may be defined for the benefit of those not accustomed to them. You don’t want to hold it crooked, cockeyed, or off level. East of that, the needle points west of true north, and has a westerly or negative declination.
A sketch is shown at the right. Then, you leensatic your protractor on the map with its center point at your current position, making sure the north-south lines on the protractor line up with the north-south lines on the map. Locate yourself and a prominent distant object on the map, and measure its magnetic bearing with the compass. The directions of true and magnetic north are indicated on the sketch.
Let’s say you see a water tower off in the distance. Telescopic sights were rarely, if ever, used on compasses. Ionospheric currents also affect the magnetic field on a diurnal basis, and during magnetic storms, but the effects on a compass are smaller than the usual errors of measurement.
The fact that they glow in the dark especially, if they’re the tritium kind which will glow for years without having to be exposed to light means you can use your compass without a light for night navigation. A typical lensatic compass is shown at the right from FM After reading those two articles anyone should be able to go out and perform basic land navigation with a map and lensatic compass.
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Another effect on the compass needle is deviationwhich is a result of local disturbances, usually magnetic rocks, masses of iron, or other effects. The sun sends ionizing ultraviolet radiation reaching the earth in about 8 minutes after it is emitted, and streams of particles, mainly protons, that take longer to reach the earth. The lensatic compass is was the typical military field compass, and is used principally to measure or lay out magnetic bearings.
A ship is swungor pointed to different azimuths, to determine the effect of induced magnetism. An “azimuth” is pretty much the same as a “bearing. FM does not mention the use of the short line, but it can probably be used to speed up the setting of an azimuth by saving 15 clicks.