Posted: 5/12/2010 3:46:07 PM EDT
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I have seen it explained several times but I am still a little foggy on it. If my area has 8 degrees west declination, does that mean that actual pole is 8 degrees west of the direction of the needle? Do I adjust my declination scale so the N is pointing 8 degrees west of the needle? |
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Quoted: West declination is ADDED to your bearing. If you want to travel 150 degrees, you would actually travel 158 degrees by compassif you have 8 degrees West declination. You can adjust your compass if you wish, I just do it in my head when I am orienterring. So true north is to the east of magnetic north in my area? |
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Quoted:
Quoted:
West declination is ADDED to your bearing. If you want to travel 150 degrees, you would actually travel 158 degrees by compassif you have 8 degrees West declination. You can adjust your compass if you wish, I just do it in my head when I am orienterring. So true north is to the east of magnetic north in my area? correct. |
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To go one further, it always helps to calibrate your compass to make sure it's ACTUALLY pointing the right way. When I was in the military we broke out all the compass's and 1/4 of them couldn't hold +/- 3 degree's, some were REALLY bad.
ETA for most people it would never matter, but since you're asking about declination, might as well make sure everything's right. |
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Quoted: To go one further, it always helps to calibrate your compass to make sure it's ACTUALLY pointing the right way. When I was in the military we broke out all the compass's and 1/4 of them couldn't hold +/- 3 degree's, some were REALLY bad. ETA for most people it would never matter, but since you're asking about declination, might as well make sure everything's right. My bob compass is a Cammenga. It should be a decent compass.....I hope! I just want to understand declination via a specific example rather than the generalizations I see that really don't seem to make sense. If I was out west and had a few degrees of east declination, then I am compensating by pushing my north indicator east the proper number of degrees. Am I getting it? |
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batmanacw,
Magnetic North is West of True North for OH (as it is for me also in MD). At approximately Cedar Rapids, Iowa, it's close to 0 degrees declination, because Magnetic and True North are in alignment. Which means for any place east of Cedar Rapids, Magnetic north is going to be West ( to the left) of True North. ThePatriot's directions are correct, he is saying the same thing. http://www.magnetic-declination.com/ |
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Quoted:
Quoted:
To go one further, it always helps to calibrate your compass to make sure it's ACTUALLY pointing the right way. When I was in the military we broke out all the compass's and 1/4 of them couldn't hold +/- 3 degree's, some were REALLY bad. ETA for most people it would never matter, but since you're asking about declination, might as well make sure everything's right. My bob compass is a Cammenga. It should be a decent compass.....I hope! I just want to understand declination via a specific example rather than the generalizations I see that really don't seem to make sense. If I was out west and had a few degrees of east declination, then I am compensating by pushing my north indicator east the proper number of degrees. Am I getting it? Yep, you're getting it. As a practical matter, for simple land nav, across much of the eastern and central US, running without declination should get you where you're going. The typical hiker isn't going to be able to run a compass line better than 10 degrees across any appreciable distance. Check it out yourself! Head out to the woods with your GPS and compass. Take waypoint at start. Hike a 1-mile straight line using your compass with proper declination. Once you've gone that mile, project a waypoint from your start and see how close you were. You might be surprised. ETA: Which brings me to my second point. Too many people, IMO, are overly concerned with pinpoint compass precision and extremely underconcerned with distance approximation. To effectively navigate across the countryside you need to know not only the direction you need to go, but also the distance. |
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Quoted:
If I was out west and had a few degrees of east declination, then I am compensating by pushing my north indicator east the proper number of degrees. Am I getting it? ugh, i was about to agree and say yes, but, now am not exactly sure about the "pushing east" part? I think of it as negative and positive declination. In OH and MD we are negative declination, so we ADD the degrees to find true north. Like Patriot said. IF out west in California, we would be positive declination (need tomake sure that is correct assumption) , Subtracting the proper amount of degrees. edit: what Fredman said. Dead reckoning is really what gets us there, using fixed objects and connecting the dots. The terrain usually dictates the direction we travel, constantly pushing us to the right or left of where we think we are trying to go. |
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Quoted: batmanacw, Magnetic North is West of True North for OH (as it is for me also in MD). At approximately Cedar Rapids, Iowa, it's close to 0 degrees declination, because Magnetic and True North are in alignment. Which means for any place east of Cedar Rapids, Magnetic north is going to be West ( to the left) of True North. ThePatriot's directions are correct, he is saying the same thing. http://www.magnetic-declination.com/ So if I have my needle pointed at magnetic north in my area, with about 9 degrees of west declination, I need my north indicator to be adjusted to point to 9 degrees east of magnetic north. I think I am getting it. If the needle is pointing to magnetic north, the 9 degrees of declination will put true north 9 degrees east of magnetic, so if I point the center line of my compass 9 degrees easst, my cardinal points are all correct. |
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Quoted: wish I had brought a compass that had degrees on it. all the ones I travel with are just watch type. Small and light weight. Quoted: If I was out west and had a few degrees of east declination, then I am compensating by pushing my north indicator east the proper number of degrees. Am I getting it? ugh, i was about to agree and say yes, but, now am not exactly sure about the "pushing east" part? I think of it as negative and positive declination. In OH and MD we are negative declination, so we ADD the degrees to find true north. Like Patriot said. IF out west in California, we would be positive declination (need tomake sure that is correct assumption) , Subtracting the proper amount of degrees. |
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Quoted:
Quoted:
batmanacw, Magnetic North is West of True North for OH (as it is for me also in MD). At approximately Cedar Rapids, Iowa, it's close to 0 degrees declination, because Magnetic and True North are in alignment. Which means for any place east of Cedar Rapids, Magnetic north is going to be West ( to the left) of True North. ThePatriot's directions are correct, he is saying the same thing. http://www.magnetic-declination.com/ So if I have my needle pointed at magnetic north in my area, with about 9 degrees of west declination, I need my north indicator to be adjusted to point to 9 degrees east of magnetic north. YES. edit: also, You can do the rough degrees in your head.... 10, 30, 45, 90 |
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Quoted: Quoted: Quoted: batmanacw, Magnetic North is West of True North for OH (as it is for me also in MD). At approximately Cedar Rapids, Iowa, it's close to 0 degrees declination, because Magnetic and True North are in alignment. Which means for any place east of Cedar Rapids, Magnetic north is going to be West ( to the left) of True North. ThePatriot's directions are correct, he is saying the same thing. http://www.magnetic-declination.com/ So if I have my needle pointed at magnetic north in my area, with about 9 degrees of west declination, I need my north indicator to be adjusted to point to 9 degrees east of magnetic north. YES. edit: also, You can do the rough degrees in your head.... 10, 30, 45, 90 just recheck my correction of this post since i thought I had the east and west wrong. ETA: I apologize for being dense. The needle would be in the negative range when the compass is oriented properly. It would be at 351 degrees when the north is in the right position. This is what would be meant my negative. In all the explanations I have read, not one mentioned that its the needle that is moved negative or west for westerly declination. |
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Quoted: Thanks for this thread, it has been helpful to me as well. Just got a good Brunton compass and noticed it is very sensitive to metal objects nearby when shooting an azimuth. Note to self: Don't hold pocket knife and compass in same hand when taking a bearing. Just hold it next to your phone instead!  |
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The earths magnetic field is changing all the time (and it's changing at an increased tempo right now) . I'm pretty sure the USGS has a sort of up to date map with inclination and declinations. I don't remember if they update the inclination/declination map every year, or every five years. |
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Quoted:
The earths magnetic field is changing all the time (and it's changing at an increased tempo right now) . I'm pretty sure the USGS has a sort of up to date map with inclination and declinations. I don't remember if they update the inclination/declination map every year, or every five years. This ^ It changes and you need to get the current declinations. True North & Magnetic Declination - A Trick to Make it Stick Magnetic declination is an essential principle to understand when navigating your way through the wilds with map and compass. Yet it's a tricky thing to remember, at least the way it has traditionally been taught, using an addition / subtraction method. Just when you think you've grasped it, the concept floats away, like fog in the morning light. Well there is a simple, practical approach to adjusting for magnetic declination when finding your bearings. The whole explanation begins with a definition of 'north." There are 2 Norths A lot of people know that there are 2 norths in terms of maps and compasses. A map shows true north, or the Geographic North Pole where all lines of longitude meet. The earth rotates around an imaginary axis that runs through the North and South Poles. A compass needle points to magnetic north, which is determined by the earth's magnetic field. The location of magnetic north moves over time, at about 5 miles per hour. Right now it is slowly creeping around somewhere NW of Hudson's Bay in Canada, about 450 miles away from true north. Magnetic Declination The angular difference between true north and magnetic north is known as "declination," or "variation" in the aviation world. Declination is different for different parts of the globe. In Washington State, the angle of declination is 20°east. This means that magnetic north is 20° east of true north. In Tennessee the angle of declination is 0°, and in Maine, it's 20° west. Declination values can be found in the margins or legend on topographic maps. Because the point of magnetic north is constantly moving, it is important to have a recent topo map for finding your way in the woods. A similar point to remember is that compasses are calibrated for different parts of the world. So when you purchase a compass, be sure that it is intended to be used in the area of your big hiking vacations. How to Find Your Bearing Follow these steps to find your bearing: 1. Place the compass on the map with the arrow on the base plate pointing in the direction you want to go. 2. Turn the dial face of the compass so that north on the compass is parallel with north on the map. 3. Place your compass level in the palm of your hand and turn yourself until the needle in the compass aligns with the North marking on the face dial. 4. The big arrow on the base plate is now aligned with your bearing. Declination Value and Bearings - A Trick to Make it Stick If you walked 10 miles through the woods in Washington State, without factoring declination value in your bearings, you would finish over 3 miles off target. That's too much! To avoid confusion in finding bearings, keep the central principle in mind: Make map bearing = magnetic bearing. You will achieve this in the field by adjusting your bearings to compensate for magnetic declination. There are 2 ways to account for magnetic declination in finding your bearings: an adjustable compass and marking your non-adjustable compass. The easiest way is with an adjustable compass. Simply turn the declination adjustment screw on the compass to the correct value and all readings are automatically converted to true north. If it's available, it's always best to have an adjustable compass on your walk. The next best way to account for declination is to mark the declination value on your non-adjustable compass at the beginning of your journey. That's simple to do. For example, when the map indicates a declination value of 20° west, you will mark your compass dial at 340°. If the map indicates a declination value of 10° east, you will mark your compass at 10°. Make the mark with a permanent marker and erase later with rubbing alcohol. Now when you take your bearings in the field, place your compass level in the palm of your hand and turn yourself until the needle in the compass aligns with the declination marking on the face dial. Then the big arrow on the base plate will point toward your bearing and automatically compensate for magnetic declination. Outdoors Adventurer, Writer and Webmaster Will Robertson lives with his family in Little Rock, Arkansas. GM |
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Quoted:
The earths magnetic field is changing all the time (and it's changing at an increased tempo right now) . I'm pretty sure the USGS has a sort of up to date map with inclination and declinations. I don't remember if they update the inclination/declination map every year, or every five years. The FAA/DOD pubs update it yearly, which is then put into the next 56 day update. OTOH, here in the SE, no one really cares unless surveying, etc. We are too close to the magnetic meridian. BTW, there are local magnetic disturbances that can cause errors of 10 degrees or more. Stone Mt, Ga is a famous one. |
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having lots of QUOTE problems..........sorry ++++++++++++++++++++++++++++++++++++++++++++++++++This is the big picture ––understand this first: There are 2 Norths A map shows true north, or the Geographic North Pole where all lines of longitude meet. The earth rotates around an imaginary axis that runs through the North and South Poles. A compass needle points to magnetic north, which is determined by the earth's magnetic field. The location of magnetic north moves over time, at about 5 miles per hour. Right now it is slowly creeping around somewhere NW of Hudson's Bay in Canada, about 450 miles away from true north. Magnetic Declination The angular difference between true north and magnetic north is known as "declination" (or "variation" in the aviation world). Declination is different for different parts of the globe. In Washington State, the angle of declination is 20°east. This means that magnetic north is 20° east of true north. In Tennessee the angle of declination is 0°, and in Maine, it's 20° west. (the blue part will be important in a minute) ++++++++++++++++++++++++++++++++++++++++++ This memory item rhymes, and sounds cool, but it is dangerous––-it requires you to remember if you are starting from true or mag. I never use it. You can ignore it. +++++++++++++++++++++++++++++++++ east is least - subtract an east dec from the compass to get true west is best - add a west dec to the compass to get true heading +++++++++++++++++++++++++++++++++++++ This is the basis of all you need to know––but it can be trimmed down considerably for normal humans. you can ignore it. +++++++++++++++++++ Can Dead Men Vote Twice At Elections True Virgins Make Dull Companions At Weddings +++++++++++++++++++++++++++ THIS IS WHY YOU CAN IGNORE IT: If you know one phrase, the other direction is just the opposite, ergo reduce to: Can Dead Men Vote Twice At Elections The C and D terms apply to actually using compass error determined by professional calibration––-this doesn't apply to hikers ergo reduce to: Men Vote Twice At Elections So ....all you need to memorize is ************************ ************************Men Vote Twice At Elections MAG VARIATION TRUE ADD EAST going from MAG to TRUE>>> add east variation (declination) subtract west variation (declination) Example: your MAG compass says you are heading 340 and your area's declination(variation) is 8W (340 MAG 8W VAR ? TRUE) ADD EAST (ergo subtract west ) therefore your TRUE heading is 340-8=332 TRUE and of course, just derive the reverse direction when needed going from TRUE to MAG>>> add west variation (declination) subtract east Example: you look at the map and know you want to go due North (360). What mag heading do you go? M V T Add East >>>reverse to >>>>> T V M Add West 360TRUE 8W VAR ? MAG add west Your MAG HEADING should be 360 + 8= 368 i.e. 008 so from OHIO... face MAG north, then steer a little to the right and you'll hit the NORTH POLE |
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Quoted:
Yep, you're getting it. As a practical matter, for simple land nav, across much of the eastern and central US, running without declination should get you where you're going. The typical hiker isn't going to be able to run a compass line better than 10 degrees across any appreciable distance. Check it out yourself! Head out to the woods with your GPS and compass. Take waypoint at start. Hike a 1-mile straight line using your compass with proper declination. Once you've gone that mile, project a waypoint from your start and see how close you were. You might be surprised. ETA: Which brings me to my second point. Too many people, IMO, are overly concerned with pinpoint compass precision and extremely underconcerned with distance approximation. To effectively navigate across the countryside you need to know not only the direction you need to go, but also the distance. i disagree. try long distance bushwhacking or geocaching with a map, plotter and compass instead of a gps. after a while you get very precise. any pilot or sailor will find the geocach in short order. |
| Right now magnetic north is somewhere near Baffin Island in Canada. If I am remembering right its somewhere north and maybe a tad west of Hudsons Bay. It moves all the time and is expected someday to be over closer to Russia, but now I forget how long that is expected to take. I know I was suprised that it was not that far off. |
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Quoted:
Quoted:
Yep, you're getting it. As a practical matter, for simple land nav, across much of the eastern and central US, running without declination should get you where you're going. The typical hiker isn't going to be able to run a compass line better than 10 degrees across any appreciable distance. Check it out yourself! Head out to the woods with your GPS and compass. Take waypoint at start. Hike a 1-mile straight line using your compass with proper declination. Once you've gone that mile, project a waypoint from your start and see how close you were. You might be surprised. ETA: Which brings me to my second point. Too many people, IMO, are overly concerned with pinpoint compass precision and extremely underconcerned with distance approximation. To effectively navigate across the countryside you need to know not only the direction you need to go, but also the distance. i disagree. try long distance bushwhacking or geocaching with a map, plotter and compass instead of a gps. after a while you get very precise. any pilot or sailor will find the geocach in short order. My comments referenced simple land nav, like getting yourself back to civilization when you're lost in the woods. Geocaching is a very different animal. And again, distance estimation is an extremely critical skill that many don't concern themselves with. |
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Quoted: Quoted: West declination is ADDED to your bearing. If you want to travel 150 degrees, you would actually travel 158 degrees by compassif you have 8 degrees West declination. You can adjust your compass if you wish, I just do it in my head when I am orienterring. So true north is to the east of magnetic north in my area? Magnetic north is in northern Canada. For us, Batman we have west declination in our area. The saying is," West is best and East is least" meaning add to your bearing for west and subtract for eastern declination. I'm here to tell you that when you're tired, hungery, cold and wet, your math skills go out the window. It is by far better to have maps with magnetic north lines drawn on them with which you set the bezel of your compass to set a bearing. At the last of a 24 hour race, during a 4 mile straight, flat road walk heading for finish, my two friends and I couldn't add up our score which was simple addition of sets of ten. Each of us tried with different results. Then we tried as a team with one guy remembering sums of sets. Still got two different answers. We are all toolmakers who deal with numbers everyday. I couldn't believe how much of a nose dive our cognative skills took. I would never rely on math in a stress situation, if I didn't have to. I also have all the dope on my rifle written down. Piss on figuring out formulas when you're in the shit. |
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Quoted: Quoted: Quoted: To go one further, it always helps to calibrate your compass to make sure it's ACTUALLY pointing the right way. When I was in the military we broke out all the compass's and 1/4 of them couldn't hold +/- 3 degree's, some were REALLY bad. ETA for most people it would never matter, but since you're asking about declination, might as well make sure everything's right. My bob compass is a Cammenga. It should be a decent compass.....I hope! I just want to understand declination via a specific example rather than the generalizations I see that really don't seem to make sense. If I was out west and had a few degrees of east declination, then I am compensating by pushing my north indicator east the proper number of degrees. Am I getting it? Yep, you're getting it. As a practical matter, for simple land nav, across much of the eastern and central US, running without declination should get you where you're going. The typical hiker isn't going to be able to run a compass line better than 10 degrees across any appreciable distance. Check it out yourself! Head out to the woods with your GPS and compass. Take waypoint at start. Hike a 1-mile straight line using your compass with proper declination. Once you've gone that mile, project a waypoint from your start and see how close you were. You might be surprised. ETA: Which brings me to my second point. Too many people, IMO, are overly concerned with pinpoint compass precision and extremely underconcerned with distance approximation. To effectively navigate across the countryside you need to know not only the direction you need to go, but also the distance. Amen, brother. Although with some practice, you can hold a pretty good bearing. There's not much need, though. There are different techniques, e.g. handrails, stoppers, boundries, etc. Distance estimation is where everybody falls down. You always believe you've gone farther than you actually have. Pace Counting, learn it, live it, love it. Over different terrain, through brush, briars, over hills, in the sand, in the creek. |
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This is a link to the Land Navigation field manual, hopefully it take you to the right part:
http://www.globalsecurity.org/military/library/policy/army/fm/3-25-26/ch6.htm#fig6-9 Look at the diagrams 6-9 through 6-15, and notice what they are doing. They are drawing an arbitrary line that is roughly perpendicular at the base of the true north-magnetic north ray diagram. They then draw an arc from the arbitrary line on the right side of the diagram to the true north ray, and another arc to the magnetic north ray. At this point you have one arc that is longer than the other arc. All you need to do now is to go from the bearing you have, (let's say it is magnetic), to the bearing you need (true), do you need to add or subtract to make the arc you have the same length as the arc you need. This is simpler than it sounds, once you understand the concept you should be able to picture it in your head. Also keep in mind that the 0 declination line roughly lines up with the Mississippi River. If you are a fair distance east or west from the Mississippi, magnetic north will lean towards the Mississippi. This works in the US, it may not work in other parts of the world. |
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Here is a map that shows the movement of magnetic north from the year 1600 through year 2000.
Map of the Movement of Magnetic North 1600 - 2000 |