Kjetil Kjernsmo ' s illustrated guide on How to use a compassMagnetic DeclinationUnfortunately , sometimes , for some quite often , it is even more complicated . There is something called magnetic declination . You see , the compass is pointing towards the magnetic northpole , and the map is pointing toward s the geographic northpole , and that is not the same place . To make things even more complicated , there is on most hiking - maps something ( that is very useful ) called the UTM - grid . This grid doesn ' t have a real north pole , but in most cases , the lines are not too far away from the other norths . Since this grid covers the map , it is convenient to use as meridians . On most orienteering maps ( newer than the early 70 ' s ) , this is corrected , so you won ' t have to worry about it . But on topographic maps , this is a problem . First , you ' ll have to know how large the declination is , in degrees . This depends on where on the earth you are . So you will have to find out before you leave home . Or somewhere on the map , it says something about it . one thing you have to remember in some areas , the declination changes significantly , so you ' ll need to know what it is this year . If you are using a map with a " UTM - grid ", you want to know how this grid differs from the magnetic pole . When you are taking out a course , you will do that more or less as described in lesson 2 , but this time , you must also look out so that you don ' t align the orienting lines with the grid lines pointing west or east , or south for that matter . When you have taken out a course like you ' ve learned , you must add or subract an angle , and that angle is the angle you found before you left home , the angle between the grid lines or meridians and the magnetic north . The declination is given as e . g . " 15 degrees east ". When you look at the figure , you can pretend that plus is to the right , or east , and minus is to the left and west . Like a curved row of numbers . So when something is more than zero you ' ll subtract to get it back to zero . And if it is less , you ' ll add . So in this case you ' ll subtract 15 degrees to the azimuth , by turning the compass housing , according to the numbers on the housing . Now , finally , the direction of travel - arrow points in the direction you want to go . Again , be careful to aim at some distant object and off you go . You may not need to find the declination before you leave home , actually . There is a fast and pretty good method to find the declination whereever you are . This method has also the advantage that corrects for local conditions that may be present ( I am thankful towards Jim Cross who pointed this out to me ) . This is what you do : Determine by map inspection the grid azimuth from your location to a know , visible , distant point . The further away , the more accurate it gets . This means you have to know where you are , and be pretty sure about one other feature in the terrain . Sight on that distant point with the compass and note the magnetic azimuth . You do that by turning the compass housing so that it is aligned with the needle . You may now read the number from the housing where it meets the base of the direction of travel - arrow . Compare the two azimuths . The difference is the declination . Update as necessary . You shouldn ' t need to do this very often , unless you travel in a terrain with lots of mineral deposits . There are a few riddles and rhymes to help you remember whether you should add or subtract . I don ' t know them . If you live in an area where you don ' t go far for it to change between east and west , it is so small you wouldn ' t need to worry about it anyway . So it ' s best to just remember whether you should add or subtract . Nevertheless , I have collected some of the rhymes people use . UncertaintyYou can ' t always expect to hit exactly what you are looking for . In fact , you must expect to get a little off course . How much you get off course depends very often on the things around you . How dense the forest is , fog , visibility is a keyword . And of course , it depends on how accurate you are . You do make things better by being careful when you take out a course , and it is important to aim as far ahead as you can see . In normal forest conditions we say that as a rule of thumb , the uncertainty is one tenth of the distance traveled . So if it is like in the figure , you go 200 meters on course , it is possible that you end up a little off course , 20 meters or so . If you ' re looking for something smaller than 20 meters across , there is a chance you ' ll miss . If you want to hit that rock in our example you ' ll need to keep the eyes open ! In the open mountain areas , things are of course a lot easier when you can see far ahead of you . This was the last of the lessons you should know . But more lessons are upcoming . Now it is time to log out and get into the backyard , and then backcountry . Try it out ! That is after all , the only way to learn this properly . Good Luck ! I said navigating in the mountains is easier . Well that is until the fog comes . Fog can make orienteering in the mountains and in the forest extremely difficult , and therefore , it can also be dangerous to the unexperienced . The principles of orienteering are still the same , but there are a few hints in the next lesson that will help you get trained . Kjetil Kjernsmo © 1997 kjetikj @ astro . uio . no 사업자 정보 표시 마루 프레스 | 백건우 | 경기도 양평군 서종면 정배리 중미산 로 851 번 길 14 | 사업자 등록 번호 : 132 - 92 - 57241 | TEL : 070 - 7787 - 5602 | Mail : marupress @ gmail . com | 통신 판매 신고 번호 : 제 2013 - 경기 양평 - 1033 호호 | 사이버 몰의 이용 약관 바로 가 기