Magnetic Declination Demystified

the levy is gone and there's no one here to help you now hi I'm John McCain from survival resources today I wanted to do a short video in regard to a subject that deals with map and compass I've talked to a lot of people over the years and it seems like one of the most confusing aspects of using a compass with the map is magnetic declination so I'm calling this tape today magnetic declination demystified and what I'd like to do is put this in very easy terms for you to understand and explain to you what it is and how it works and that way people will no longer be confused in regard to this magical declination or magnetic declination first of all what you have to understand is there are two North's when you start working with a map and compass there is true north and then there is a magnetic north now most of your maps at the top of the map will be true north this is also known as geographic north this is actually 1200 miles north of magnetic north so as you can see here there's a difference between the true north the top of your map and magnetic north which by the way is where the needle on your compass points so they're always going to be off the map is going to be straight up and down your compass is going to be facing to wherever the magnetic north is now the difference between these two is called declination the declination is the variance between your true north and your magnetic north what we have to do when using a compass with a map is we have to adjust for this declination for this variance between the true north and the magnetic north now let me give you a close-up of what we call an isogonic chart this is going to show you how these declination lines work and how they move as you move around the country okay as you can see here we have the what is called the isogonic chart what this chart does is show you the variants in declination between your true or geographic north and your magnetic north right here we have a line which has zero on it that is because this is the a Ghana Klein a gon I see this is the iconic line because at this point on this line both the geographic or True North aligns with magnetic north so there is no variance if you were on this line in the United States you also would not have to adjust your compass for magnetic declination because there is zero declination okay you will notice now as we move east of the agonic line your degrees of variance increase the further you get from the line you will also note that these lines lean to the left they lean to the left which makes them what we call westerly declination if you were east of the agonic line you have westerly declination as you move to the west of the agonic line again you will see that these degrees of variance increase rapidly you also notice that these lines lean to the right so if you are west of the agonic line you have easterly declination if you were east of the agonic line you have westerly declination sometimes this confuses people because they say well I'm in the east or well I'm in the West it has nothing to do with where you are it has to do with which way the magnetic declination lines lead so if you were east they lean left or west if you are west they lean right or east it's that simple okay I hope that isogonic chart has helped explain this a little bit to you in regard to magnetic declination and basically what this means is let me move to the East Coast here ok run to East Coast our map is always facing straight up the top of the map amo stories on most maps are Geographic or TrueNorth but your compass is going to move towards magnetic door so if I'm on the East Coast the top of the map is here but my compass magnetic needle is going to be facing over here if you move to the west coast over here again the top of the map is going to be true north geographic north however your magnetic needle is going to point this direction so as you can see the magnetic needle unless you're on that agonic line is going to be different than the top of your map so we really have to adjust for this if you're using your compass with your map now there's two ways to do this one way is you can adjust your compass the second way is you can adjust your map let's discuss the compass first some compasses they have a means on them in which to adjust for declination you can manually adjust it and then you don't have to worry about it one of the things I don't like about doing that with the compass is it's only good for that area that you're in at that specific declination or variance if you move to another area or you move off that map to another map now that your declination is going to change so now you have to remember to go in there and change that declination adjustment on your compass otherwise it's going to be off ok the second way to do it is to adjust the compass manually and you would do this by either adding or subtracting now we've already indicated if you're over here on the East Coast your map top is going to be up here your compass is going to be facing this direction so you're going to have to add the declination degrees let's use 15 degrees as an example in order to bring the magnetic compass in line with the top of the map and if you're on the west coast over here again we know your magnetic needle is facing this way you're going to have to subtract that degrees 15 degrees in this case in order to bring it online with your TrueNorth on the map now people sometimes can't remember whether to add or subtract or how to do this it's pretty easy to remember once you understand the basic principles of this there's various ways to adjust it by adding or subtracting not various ways to do it there's only one way to do it but you have to remember that there's a lot of let's say cute little sayings out there like East is least and west is best in this type of thing and I really don't get too involved with trying to remember those if you remember your declination and you remember which way the needle leans you're going to remember which way to adjust your dial in regards to either adding or subtracting but there's a much easier way every time you use your compass with the map your map will tell you whether to turn your dial left or right now I'm going to show you how this works okay as you can see here on the bottom of this map is what we call the declination diagram it's in the center of the left side of a map what I have done is made a large drawing of this for the purpose of this discussion this is the larger diagram this would be on a map that has westerly declination because it is east of the agonic line this one would be a declination diagram that has easterly declination because it's west of the agonic line now what this thing tells you you will notice this is where the stars are or true north this is magnetic north this is grid north which for the purpose of this discussion you can ignore these are the two lines we're dealing with our true north and our magnetic north as you can see in this case we have a 15 degree declination okay what this tells you is that magnetic north is 15 degree from True North what this also tells you is how to turn your dial you will notice that this is to the left of True North so what you would do in this case let's bring up my trusty compass what you do in this case is you would turn your dial to the left 15 degrees when you turn this 15 degrees you will now notice that your magnetic needle is pointing to magnetic north but your line of travel is facing true north on your map so when you are on the East Coast or if you were east of the agonic line with westerly declination all you have to do is look at this at the bottom of your map and you would turn your dial to the right this is a means in which to edge you would notice we added 15 degrees but instead of remembering to add just look at the diagram on the map and it'll tell you turn the wheel to the left again if you're on the west coast you will see that it is to the right so you would turn your wheel to the right ok say here you would go 15 degrees you would subtract 15 degrees but you instead of remembering to subtract just turn your housing to the right and now you can see that when you turn that to the right your magnetic needle is facing magnetic north but your direction of travel is heading true north which will correspond with your map which has north and south lines on it quadrillion lines so this is an easy way to remember if your east of the agonic line with westerly declination turn your wheel in the direction from true north to magnetic north you would turn your wheel left if you're on the Left diagram here which is easterly declination west of the agonic line you can see you would turn your wheel or your housing right whatever degrees is indicated on the bottom of a map okay as you can see if you use the declination diagram at the bottom of your map you don't have to remember whether it's an add or subtract what do you have to do is look at the diagram and it will tell you whether to turn your compass housing to the left or to the right I find it much easier to remember this way because your map is always with you if you're using your map with compass I've had people say well what if I don't have a map well if you don't have a map you don't have to worry about adjusting for declination you're only using your compass to stay on a straight line so declination doesn't fall into this problem it's only when you're using your compass with the map now myself I don't care to adjust the compass for declination and I'll explain to why first of all if you do it manually and you take that compass to another area you have to remember to change to the new degree of declination for that area not so bad but if you're adding or subtracting the degrees the declination you have to do it for every bearing that you shoot for every bearing or every asmath now I use those two words interchangeably in the Marine Corps we used azmuth and now in orienteering we use bearing that they both mean the same thing so whatever word I use bear with me okay one other thing I didn't mention so far and this confuses it a little more is if you're taking a reading from your map that you're going to use in the field then you're going to do what we've discussed so far you're going to add or subtract or turn your housing to the left or to the right depending on whether you're east or west of the agonic line keep in mind though that if you shoot a bearing in the field with your compass and now you want to put that on your map you have to do just the opposite so this confuses it even more as a quick example your east of the ahna Klein like I am in New York so we have westerly declination okay we have to compensate for that by adding the 15 degrees if that's what the degrees are here where I am okay but that's only if I'm taking a reading from my map and going to use it in the field now if I happen to be out in the field and I shoot myself a bearing or an azmuth and I want to transfer that to my map I have to do just the opposite now I have to subtract as you can see it gets a little confusing and I think there's a better way to do this and I'm going to show you that next if you adjust your map for declination you do it once you adjust every map you have like I do and then you never have to worry again about adjusting your compass for declination you use your compass just the way it came out of the box and you never have to worry about it I think this is a much better way for people to do things much easier way much less confusing way let me show you how to map a mark or mark a map so that you can adjust it protect one a ssin and then you never have to worry about this again okay what I have here is a map as you can see back at the bottom here we have our declination diagram again now there's a lot of maps out there that have north and south lines they run from top to bottom straight up and down these are called meridian lines however that's what you're going to use on a map or the side line here if you adjust your compass for declination but this here is showing us how we don't have to do that you will notice here in the declination diagram this here says twelve and a half degrees and the magnetic north is to the left of true north now this is your degree of declination what I want to warn you about is that although a lot of these are accurate some of them are not what I like to do with all my maps is get myself a little a compass protractor okay and I set this on here I check to make sure this is true before I start drawing any lines on my map because this is what we're going to use to draw our first line so just as a word of warning always make sure that the diagram is accurate before you start using it then what you're going to do is you're going to get yourself a long metal ruler or some type of a wide ruler like this I like a ruler about this wide to do this and you're going to line it up with the line of magnetic declination down here on your declination diagram and then you're going to draw a line the length of the map now I'm going to zoom back here and show you how to do this okay as you can see we started our first line right alongside the magnetic declination line at the bottom I just showed you a close-up of that so what you're going to do is get yourself a good long ruler and you're going to draw a line the length of the map at that angle and then you're going to draw a line on the other side of your ruler to do the same that will give you two lines now all you have to do then is use the width of the ruler and keep drawing lines to the left using the previous line and the same way over here you will continue to the right using the width of the ruler and every one of these lines now on your map is going to be at the declination that's indicated at the bottom now the advantage of this is when you go to use a compass we've grabbed my compass I'm not going to get into a class on map and compass here but now instead of using meridian lines or the slide everything you're going to use is based on these declination lines okay when you adjust your compass and you move your dial so that the Meridian lines are on line you want them on line with these declination lines it is that simple once you adjust your map for declination like this you never have to worry about this again you don't have to change the dial at all on your compass you just use the map though you would any other time using these declination lines to me this is so much easier than using any type of an adjustment under compass because once you mark this map it's done mark every one of them you can do this on a dining room table and once you fold it up you have it with you you're good to go we're there you have it I hope I've helped to demystify magnetic declination for you it is important people wonder why this is so important it's because the further you get from the agonic line the more these degrees the declination increase what you have to understand is if you're only five degrees off now keep in mind most compasses only have a two degree accuracy so if you're five degrees off in one mile you're going to be 0.35 miles off from your destination if you go five miles you're going to be one point seven six miles off and if you go ten miles you're going to be three-and-a-half miles off your destination so as you can see as the distance increases this declination means more and more to you okay I hope that by explaining declination what it is and how it works you have a better idea myself I adjust my maps I think it's a lot easier to worry about adding and subtraction but you do what's best for you anyway as always I thank you for joining us today I hope you'd like to go check out our website at survival resources com we have a lot of products on there and we have a lot of articles in other videos that you can watch anyway thanks for being there for us and my wife Denise and we'll catch you next time around

Channel: survivalresources

Views: 241,199

Rating: 4.9136524 out of 5

Keywords: Compass, Map, Magnetic Declination, Magnetic Variance, Survival Resources, Survival, Resources, John D. McCann, Using Map with Compass

Id: peu7uMp0cVU

Length: 19min 51sec (1191 seconds)

Published: Sun Nov 10 2013