I suppose I should post one on topic post before I head out.
Non hikers are about a psi shy of a legal ball.
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The Compass thread
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BirdBrain wrote:
Hey ATM, I made some progress over here:
Sawyer Squeeze
Just helping you find it. I expected a comment last night. I saw you looking at it. It is rev 1 of the mini system. It will likely be improved... especially if people criticize it.
I was checking it. I'll go over and see what I can criticize.
Changes Daily→ ♪♫♪♫♪♫♪♫ ♪♫♪♫♪♫ ← Don't blame me. It's That Lonesome Guitar. -
BirdBrain wrote:
hikerboy wrote:
BirdBrain wrote:
Hey ATM, I made some progress over here:
Sawyer Squeeze
Just helping you find it. I expected a comment last night. I saw you looking at it. It is rev 1 of the mini system. It will likely be improved... especially if people criticize it.
how do you use the sawyer squeeze to navigate?
I hang it from a tree. Mark where the bottom of the shadow strikes the ground. Wait 15 minutes and make another mark. This gives you the east west line. Bisect that line and you have north south. Carefully dig up your creation and carry it on a flat surface as you hike out.
Or go up to a guy with a compass and say "hey, I give you a really nice filter if you let me use your compass". -
I have a declination question. I think I understand what it is but can't figure out how to program it into my watch.
First, lets clarify...please correct me if I'm wrong!
Declination is the angle between magnetic north and the North Pole
Areas east of the Agonic line are expressed in the negative form
Areas west of the Agonic line are expressed in the positive form
If you are east of the Agonic line, your compass needle will pull towards the west (or to the left)
If you are west of the Agonic line, your compass needle will pull towards the east (or to the right)
So, around Knoxville TN and navigating with a cheap compass, North will always be too far to the west (if I don't sync the compass), so I will have to adjust and move more to the east?
Back to the watch. I can't figure out how to correctly express declination for Knoxville TN. I can use either East or West and only a positive number expressed in this form... xx.x*. I can only do 0.5 to 99.5
I think the declination for Knoxville is -5.50* East.
What exactly does -5.50* East mean..that my compass will pull 5* towards west?
Does any of this make sense?
Lost in the right direction. -
You have it fine........... The watch part I can't help you.
Cheesecake> Ramen
-
It makes perfect sense, but I do occasionally teach this stuff.
Usually you will use EITHER the arithmetic sign OR the word 'East' or 'West', not both. Tennessee, like all the rest of Appalachia, does indeed have a westward declination, so your compass will point west of true north. The agonic line, or nullcline, runs nearly down the Mississippi River. Thunder Bay, the Quad Cities, St. Louis, Memphis and Biloxi all have declination that is close to zero.
[IMG:http://www.summitpost.org/images/medium/358202.jpg]
If you have a direction measured from a line of longitude on a map, that's a true direction. It's measured clockwise from north, so east is 90°, south is 180°, west is 270°.
To make a true direction into a compass direction, the mnemonic is:
Timid Virgins Make Dull Company At Weddings
which is:
- take the True direction
- adjust for Variation (your 5.5°)
- gives a Magnetic direction
- adjust for Deviation (zero for a handheld compass, but will be significant in a vehicle, ship, or aircraft and must be measured.
- gives a Compass direction
- Add West - which means add if the variation or deviation is West, subtract if it's East.
So if you measure, say, 45° on a map, True (45°) + (Add West) Variation (5.5°) = Magnetic (50.5°). Your magnetic heading would be 50.5° (and for a handheld compass clear of metal objects, the deviation will be negligible, so your compass heading will be negligible as well).
To go the other way, for instance if you've taken a compass sight and want to draw it on the map, the rule is:
Chicago Dead Men Vote Twice At Elections
which is:
- take the Compass heading
- adjust for Deviation (again, negligible for a handheld compass in the field)
- gives a Magnetic direction
- adjust for Variation (your 5.5°)
- gives the True direction
- Add East - add if the variation or deviation is East, subtract if it's West
Compass (3°) - (Add East, and the variation is West) Variation (5.5°) = True (-1.5°). This is less than 360°, so add 360° to get 358.5°.
I recommend that newbies get a compass with an adjustable declination[1] (this has become a cheap feature, so a lot of compasses have it), adjust it to the area where they intend to hike, and then work with True directions throughout, changing only when they're hiking outside their home turf. We do well in the field to sight within a degree or two of error, so even the map above will give a reasonable idea of the figure to use. Then, as long as you're using an adjustable compass, there's no worry about getting the arithmetic right, which can be particularly challenging if you're disoriented, the weather is bad, and you're tired - just the conditions you're likely to be under when you're trying to become un-lost. So, for example, living near Albany, New York, I just leave my compass set on 14° West. That' setting is Close Enough for the Adirondacks, the Catskills, and anywhere along the AT from Delaware Water Gap to Maine Junction. I pretty much never hike outside that area at the moment. I'll have to remember to reset it if I ever travel down your way.
The classes that ADK offers teach this method, and for ADK trips in winter or off trail, the participants are required to have an adjustable-declination compass unless they can demonstrate that they're already proficient in another method.
An alternative, that a lot of teachers prefer, is to work in magnetic directions throughout. This is easier if, when you first get a map, you lay it out, take a long straightedge, and scribe lines a couple of inches apart all over it that run magnetic north and south. When you are plotting a direction on the map, you can lay your protractor along one of these lines. Pilots are taught this method, and things like airport runway headings and directions from navigational aids are all quoted as magnetic directions. I like this less well because you have to prepare every map, rather than preparing your compass once.
I'm comfortable with all three methods (adjustable compass, scribed map, arithmetic), but I think the method of using an adjustable compass and working in true directions is the one that I'm least likely to screw up in a bad situation when I'm addled.
= = = = =
[1] I mean an actual compass with a swinging magnet in it. What's the battery life on your compass watch? How repeatable are its measurements? Does its variation change depending on what other functions of the watch are active? And (most important to me) how do you sight it? If all you care is, "is the trail I'm on heading in approximately the right direction," then you don't even need to worry about compass variation. If you're depending on a compass enough to need the variation set, then you need one you can sight accurately.I'm not lost. I know where I am. I'm right here. - take the True direction
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Thank you! I understand most of this but will have to think about the math a little more. Based on your explanation, I believe that the declination on my watch should be set to "East 5.50"
AnotherKevin wrote:
It makes perfect sense, but I do occasionally teach this stuff.
Usually you will use EITHER the arithmetic sign OR the word 'East' or 'West', not both. Tennessee, like all the rest of Appalachia, does indeed have a westward declination, so your compass will point west of true north. The agonic line, or nullcline, runs nearly down the Mississippi River. Thunder Bay, the Quad Cities, St. Louis, Memphis and Biloxi all have declination that is close to zero.
[IMG:http://www.summitpost.org/images/medium/358202.jpg]
If you have a direction measured from a line of longitude on a map, that's a true direction. It's measured clockwise from north, so east is 90°, south is 180°, west is 270°.
To make a true direction into a compass direction, the mnemonic is:
Timid Virgins Make Dull Company At Weddings
which is:
- take the True direction
- adjust for Variation (your 5.5°)
- gives a Magnetic direction
- adjust for Deviation (zero for a handheld compass, but will be significant in a vehicle, ship, or aircraft and must be measured.
- gives a Compass direction
- Add West - which means add if the variation or deviation is West, subtract if it's East.
So if you measure, say, 45° on a map, True (45°) + (Add West) Variation (5.5°) = Magnetic (50.5°). Your magnetic heading would be 50.5° (and for a handheld compass clear of metal objects, the deviation will be negligible, so your compass heading will be negligible as well).
To go the other way, for instance if you've taken a compass sight and want to draw it on the map, the rule is:
Chicago Dead Men Vote Twice At Elections
which is:
- take the Compass heading
- adjust for Deviation (again, negligible for a handheld compass in the field)
- gives a Magnetic direction
- adjust for Variation (your 5.5°)
- gives the True direction
- Add East - add if the variation or deviation is East, subtract if it's West
Compass (3°) - (Add East, and the variation is West) Variation (5.5°) = True (-1.5°). This is less than 360°, so add 360° to get 358.5°.
I recommend that newbies get a compass with an adjustable declination[1] (this has become a cheap feature, so a lot of compasses have it), adjust it to the area where they intend to hike, and then work with True directions throughout, changing only when they're hiking outside their home turf. We do well in the field to sight within a degree or two of error, so even the map above will give a reasonable idea of the figure to use. Then, as long as you're using an adjustable compass, there's no worry about getting the arithmetic right, which can be particularly challenging if you're disoriented, the weather is bad, and you're tired - just the conditions you're likely to be under when you're trying to become un-lost. So, for example, living near Albany, New York, I just leave my compass set on 14° West. That' setting is Close Enough for the Adirondacks, the Catskills, and anywhere along the AT from Delaware Water Gap to Maine Junction. I pretty much never hike outside that area at the moment. I'll have to remember to reset it if I ever travel down your way.
The classes that ADK offers teach this method, and for ADK trips in winter or off trail, the participants are required to have an adjustable-declination compass unless they can demonstrate that they're already proficient in another method.
An alternative, that a lot of teachers prefer, is to work in magnetic directions throughout. This is easier if, when you first get a map, you lay it out, take a long straightedge, and scribe lines a couple of inches apart all over it that run magnetic north and south. When you are plotting a direction on the map, you can lay your protractor along one of these lines. Pilots are taught this method, and things like airport runway headings and directions from navigational aids are all quoted as magnetic directions. I like this less well because you have to prepare every map, rather than preparing your compass once.
I'm comfortable with all three methods (adjustable compass, scribed map, arithmetic), but I think the method of using an adjustable compass and working in true directions is the one that I'm least likely to screw up in a bad situation when I'm addled.
= = = = =
[1] I mean an actual compass with a swinging magnet in it. What's the battery life on your compass watch? How repeatable are its measurements? Does its variation change depending on what other functions of the watch are active? And (most important to me) how do you sight it? If all you care is, "is the trail I'm on heading in approximately the right direction," then you don't even need to worry about compass variation. If you're depending on a compass enough to need the variation set, then you need one you can sight accurately.
Question... Is the Agonal line also called "The Meridian Line" or is it one of the 12 main meridian lines?
My watch has a digital compass with a magnetic North indicator and a bearing indicator that can be locked in place. It displays the heading in degrees and cardinals. The battery life is 14 days in Time mode, or 10/15/100 hrs in GPS mode depending on accuracy. I don't understand the question about the repeatable measurements (?). I don't think the variation changes when other functions are being used...the compass is always accessible when using other functions.
I will mainly use it to supplement maps to ensure I'm heading in the right direction...it will never be a primary means of navigation (but I still like knowing how this stuff works.)Lost in the right direction. - take the True direction
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AK, lets pretend for a moment that the whites don't exist.
as a practical matter, if you were to get lost on the AT, can you ignore declination as you figure out how to get back to the trail/civilization?
my guess is that you can, but i've never been lost so i haven't been able to test my theory.2,000 miler -
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
-
My guess is that you can, also. And you can ignore sighting quality as well. A toy compass, as long as it points north, is probably fine for that purpose.
max.patch wrote:
AK, lets pretend for a moment that the whites don't exist.
as a practical matter, if you were to get lost on the AT, can you ignore declination as you figure out how to get back to the trail/civilization?
my guess is that you can, but i've never been lost so i haven't been able to test my theory.
But I've never been one for staying on the trail.I'm not lost. I know where I am. I'm right here. -
I'm a visual learner...that map tells it all...thanks.
AnotherKevin wrote:
It makes perfect sense, but I do occasionally teach this stuff.
Usually you will use EITHER the arithmetic sign OR the word 'East' or 'West', not both. Tennessee, like all the rest of Appalachia, does indeed have a westward declination, so your compass will point west of true north. The agonic line, or nullcline, runs nearly down the Mississippi River. Thunder Bay, the Quad Cities, St. Louis, Memphis and Biloxi all have declination that is close to zero.
[IMG:http://www.summitpost.org/images/medium/358202.jpg]
If you have a direction measured from a line of longitude on a map, that's a true direction. It's measured clockwise from north, so east is 90°, south is 180°, west is 270°.
To make a true direction into a compass direction, the mnemonic is:
Timid Virgins Make Dull Company At Weddings
which is:
- take the True direction
- adjust for Variation (your 5.5°)
- gives a Magnetic direction
- adjust for Deviation (zero for a handheld compass, but will be significant in a vehicle, ship, or aircraft and must be measured.
- gives a Compass direction
- Add West - which means add if the variation or deviation is West, subtract if it's East.
So if you measure, say, 45° on a map, True (45°) + (Add West) Variation (5.5°) = Magnetic (50.5°). Your magnetic heading would be 50.5° (and for a handheld compass clear of metal objects, the deviation will be negligible, so your compass heading will be negligible as well).
To go the other way, for instance if you've taken a compass sight and want to draw it on the map, the rule is:
Chicago Dead Men Vote Twice At Elections
which is:
- take the Compass heading
- adjust for Deviation (again, negligible for a handheld compass in the field)
- gives a Magnetic direction
- adjust for Variation (your 5.5°)
- gives the True direction
- Add East - add if the variation or deviation is East, subtract if it's West
Compass (3°) - (Add East, and the variation is West) Variation (5.5°) = True (-1.5°). This is less than 360°, so add 360° to get 358.5°.
I recommend that newbies get a compass with an adjustable declination[1] (this has become a cheap feature, so a lot of compasses have it), adjust it to the area where they intend to hike, and then work with True directions throughout, changing only when they're hiking outside their home turf. We do well in the field to sight within a degree or two of error, so even the map above will give a reasonable idea of the figure to use. Then, as long as you're using an adjustable compass, there's no worry about getting the arithmetic right, which can be particularly challenging if you're disoriented, the weather is bad, and you're tired - just the conditions you're likely to be under when you're trying to become un-lost. So, for example, living near Albany, New York, I just leave my compass set on 14° West. That' setting is Close Enough for the Adirondacks, the Catskills, and anywhere along the AT from Delaware Water Gap to Maine Junction. I pretty much never hike outside that area at the moment. I'll have to remember to reset it if I ever travel down your way.
The classes that ADK offers teach this method, and for ADK trips in winter or off trail, the participants are required to have an adjustable-declination compass unless they can demonstrate that they're already proficient in another method.
An alternative, that a lot of teachers prefer, is to work in magnetic directions throughout. This is easier if, when you first get a map, you lay it out, take a long straightedge, and scribe lines a couple of inches apart all over it that run magnetic north and south. When you are plotting a direction on the map, you can lay your protractor along one of these lines. Pilots are taught this method, and things like airport runway headings and directions from navigational aids are all quoted as magnetic directions. I like this less well because you have to prepare every map, rather than preparing your compass once.
I'm comfortable with all three methods (adjustable compass, scribed map, arithmetic), but I think the method of using an adjustable compass and working in true directions is the one that I'm least likely to screw up in a bad situation when I'm addled.
= = = = =
[1] I mean an actual compass with a swinging magnet in it. What's the battery life on your compass watch? How repeatable are its measurements? Does its variation change depending on what other functions of the watch are active? And (most important to me) how do you sight it? If all you care is, "is the trail I'm on heading in approximately the right direction," then you don't even need to worry about compass variation. If you're depending on a compass enough to need the variation set, then you need one you can sight accurately.
I may grow old but I'll never grow up. - take the True direction
-
TrafficJam wrote:
Thank you! I understand most of this but will have to think about the math a little more. Based on your explanation, I believe that the declination on my watch should be set to "East 5.50"
Question... Is the Agonal line also called "The Meridian Line" or is it one of the 12 main meridian lines?
My watch has a digital compass with a magnetic North indicator and a bearing indicator that can be locked in place. It displays the heading in degrees and cardinals. The battery life is 14 days in Time mode, or 10/15/100 hrs in GPS mode depending on accuracy. I don't understand the question about the repeatable measurements (?). I don't think the variation changes when other functions are being used...the compass is always accessible when using other functions.
I will mainly use it to supplement maps to ensure I'm heading in the right direction...it will never be a primary means of navigation (but I still like knowing how this stuff works.)
The agonic line is the imaginary line where true north and magnetic north coincide. It's the green line on this map. It wanders a lot, because the Earth's magnetic field isn't a simple one like a bar magnet, it's got small scale lumps and ripples that distort it. One of the biggest of those is called the South Atlantic Anomaly, and you can see that the lines there are pretty strangely shaped. (There's a gravitational anomaly there, too. That's the area of the planet where the sea level is highest.)
[IMG:https://upload.wikimedia.org/wikipedia/commons/thumb/1/11/World_Magnetic_Declination_2015.pdf/page1-640px-World_Magnetic_Declination_2015.pdf.jpg]
The meridian line is simply the line running true north and south from wherever you are.
In Tennessee, your magnetic variation will definitely be West. It will vary from zero to about six degrees, depending on where in the state you are. You will enter on your watch that the variation is 5.5° W (or whatever the figure was).
Repeatability: There are random errors: if you stand in the same place and sight on the same object a dozen times, how closely clustered are the answers? You will surely do no better than that in field conditions. With a mirror sight compass, I can get to within a degree 95% of the time. With a baseplate compass, and just reading the 'direction of travel' arrow or trying to sight along the edge of the baseplate, my error is probably three times that. With a good lensatic, I can get to within a half-degree or so, with a not-all-that-good surveyor's transit, to maybe 5 minutes of arc.
There are also systematic errors. I notice that my phone varies about 3° as I dim the backlight. Apparently the backlight power supply puts out a big enough magnetic field to throw the compass off that far. The compass in my old truck would swing up to about 15° when I started the engine, because the ignition put out a pretty big magnetic field. For a handheld compass, you want it at least a foot away from anything steel (like a knife or a steel zipper) on your person, at least 6-10 feet from a vehicle, at least 100 feet from a building, power line, or wire fence, because all of those things emanate magnetic fields. There are also a few spots in Harriman where a compass is just about worthless, because you're standing on iron mine tailings. The only one on the A-T there is one little area between Elk Pen and Island Pond. It's mostly a curiosity.I'm not lost. I know where I am. I'm right here. -
Makes me think I should have paid more attention when my son's were working on the Orienteering merit badge.
LIhikers wrote:
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
The road to glory cannot be followed with much baggage.
Richard Ewell, CSA General -
I shouldn't describe three methods for compass variation in the same post. Sorry.
LIhikers wrote:
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
If you're a boundary monitor, your orienteering skills are already better than the vast majority of hikers. And I'm sure you're already familiar with one of the methods. So carry on.I'm not lost. I know where I am. I'm right here. -
Actually my compass skills come from when I got my pilot license.
AnotherKevin wrote:
I shouldn't describe three methods for compass variation in the same post. Sorry.LIhikers wrote:
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
If you're a boundary monitor, your orienteering skills are already better than the vast majority of hikers. And I'm sure you're already familiar with one of the methods. So carry on.
Beside everything you mentioned, I had to compensate for the wind too. -
The only times in practice that you really need accurate sights and need to worry about compass variation are when you're navigating by sighting on a distant object.
The classic example is 'sight resection,' where you sight on 2-3 distant objects like peaks or highway intersections, and draw your sight lines on the map to determine your position. If the objects are all about a mile away, there's no big worry. A 1 degree error will put you 80 feet off, which will usually be enough to see your feature. But if they're ten miles away, the same error will put you 800 feet off, which starts to be significant.
About the only time that I can remember on a recent hike having to sight that carefully was on a bushwhack in the Catskills. We broke out to the top of a long ridge after several miles of swimming in spruce. The forest is thick there. We came to this view.
[IMG:https://farm4.staticflickr.com/3877/14738413825_f10056c98b_z.jpg]
We could find the ridge we were on using a topo, and the question was, "where on the ridge are we and how far is the canister with the summit log?" We got that answer by sighting on the summit of Ticetonyk Mountain at left, and the south end of the Ashokan bridge, visible through the tree at right. Both locations were clearly spotted on a topo, and drawing the two sight lines and the ridge line on the map gave us a location. They were far enough away (7.5 and 8 miles. respectively), that we got a probable error of well over a quarter mile when we plotted it, even doing it carefully. I was teaching the Elf this stuff, so I had him draw the lines while we ate lunch at the overlook.
That was good enough to find the canister, but gives an idea of what the extreme case is.
Much more often, here in the East, you're moving through dense woods and just need a rough indication of direction. The real navigation comes in having an eye for the terrain. In fact, on the trip in question, I'd intentionally aimed to hit the ridge about 0.4 mile away from the summit, because I knew I'd recognize reaching the ridge, and would then be certain which direction to turn. If I'd aimed for the summit directly, I wouldn't know which side I was on when I came to the ridge. Using the terrain like that, I had a natural feature to guide me in, and my errors were self correcting. And I'd aimed for the ridge in a similar way, by intentionally straying in the opposite direction until we came to the band of cliffs about 200 feet below the summit, and knowing which way to follow the cliff bases to where the slope was easier and we could get up to a saddle. It was like that for two days, intentionally veering first one way and then the other ("aiming off"), then using "handrails" to guide us in to the next point.
Hey, Elf, I know you remember that trip!I'm not lost. I know where I am. I'm right here. -
Be wise enough to walk away from the nonsense around you!
-
And I'm guessing that you're old enough that you figured the wind triangle on an E6B whiz-wheel.
LIhikers wrote:
Actually my compass skills come from when I got my pilot license.Beside everything you mentioned, I had to compensate for the wind too.AnotherKevin wrote:
I shouldn't describe three methods for compass variation in the same post. Sorry.If you're a boundary monitor, your orienteering skills are already better than the vast majority of hikers. And I'm sure you're already familiar with one of the methods. So carry on.LIhikers wrote:
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
I'm not lost. I know where I am. I'm right here. -
And aiming your walking deliberately one side of the point you want to reach. After you get near, its obvious which way to trn to get to it.
As an example: if you need to get somewhere east of your location. Triangulate, compass heading to the two points, as described in post 96 above. Aim slightly off side of the point you want to head for. Say, the north of that point. When you get near, you will be feet, or a mile or so, north of where you wanted to end up. Turn south and walk towards the point.
Another example: our radio navigation went out coming back from the Mediterranean Sea.
So, our navigator took sun and star sightings with a sextant and told the Captain if we steer a certain heading, we will get back to our home port.
The Captain had the helmsman steer several degrees south of that bearing. That way when we got back to the east coast of the US, we just turned North, as we knew we were well south of home port, and sail the ship until we reached the harbour entrance.
( No repair parts aboard ship for the LORAN.)--
"What do you mean its sunrise already ?!", me. -
Good summary! At least for Suunto and Cammenga (and IIRC Silva works the same way).
Brunton has a slightly different system, where the compass card rotates against a friction fit, and K&R has a system where the declination ring and the orienteering ring are both on the front and you can rotate them against each other.
Speaking of K&R, which is a less well-known brand:
I've been happy with my K&R Alpin compass. The construction feels a lot more robust than the lower-priced ones from Brunton, Silva and Suunto. (Cammenga's are Just Too Heavy.) The three I mentioned all seem to develop problems - way sooner than they ought to - with bubbles in the capsule or cracked or bent sighting mirrors. If you prefer a lensatic to a mirror sight, there's an Alpin Pro that's usable that way. I struggle with lensatics ever since my doc inflicted bifocals on me.
The gold standard of compasses - and it's priced accordingly - is the Brunton 5006LM. I can't afford it, and even if I could, the damn thing weighs half a pound. But it's bombproof, works anywhere in the world, and reads out at half-degree resolution. It's a great graduation present for a field geologist, mining engineer or forester.I'm not lost. I know where I am. I'm right here. -
Was that the same ship you lost radio communications, 3 of 4 boilers and 1 of 2 turbines and was hit by hurricane Camille?
JimBlue wrote:
Another example: our radio navigation went out coming back from the Mediterranean Sea.
-
that ship musta been made by general motors.
chief wrote:
Was that the same ship you lost radio communications, 3 of 4 boilers and 1 of 2 turbines and was hit by hurricane Camille?JimBlue wrote:
Another example: our radio navigation went out coming back from the Mediterranean Sea.
2,000 miler -
Your compass and Deet should never be stored in the same pocket
Cheesecake> Ramen -
I usually crab when I hike to allow for drift and poles wash.
AnotherKevin wrote:
And I'm guessing that you're old enough that you figured the wind triangle on an E6B whiz-wheel.LIhikers wrote:
Actually my compass skills come from when I got my pilot license.Beside everything you mentioned, I had to compensate for the wind too.AnotherKevin wrote:
I shouldn't describe three methods for compass variation in the same post. Sorry.If you're a boundary monitor, your orienteering skills are already better than the vast majority of hikers. And I'm sure you're already familiar with one of the methods. So carry on.LIhikers wrote:
I used to know how to use a compass and map.......then I read Kevin's explanation.
Now I'm confused
-
or rubber worms.
CoachLou wrote:
Your compass and Deet should never be stored in the same pocket
-
...except they put Kentucky where Tennesee use to be.
Drybones wrote:
I'm a visual learner...that map tells it all...thanks.AnotherKevin wrote:
It makes perfect sense, but I do occasionally teach this stuff.
Usually you will use EITHER the arithmetic sign OR the word 'East' or 'West', not both. Tennessee, like all the rest of Appalachia, does indeed have a westward declination, so your compass will point west of true north. The agonic line, or nullcline, runs nearly down the Mississippi River. Thunder Bay, the Quad Cities, St. Louis, Memphis and Biloxi all have declination that is close to zero.
[IMG:http://www.summitpost.org/images/medium/358202.jpg]
If you have a direction measured from a line of longitude on a map, that's a true direction. It's measured clockwise from north, so east is 90°, south is 180°, west is 270°.
To make a true direction into a compass direction, the mnemonic is:
Timid Virgins Make Dull Company At Weddings
which is:
- take the True direction
- adjust for Variation (your 5.5°)
- gives a Magnetic direction
- adjust for Deviation (zero for a handheld compass, but will be significant in a vehicle, ship, or aircraft and must be measured.
- gives a Compass direction
- Add West - which means add if the variation or deviation is West, subtract if it's East.
So if you measure, say, 45° on a map, True (45°) + (Add West) Variation (5.5°) = Magnetic (50.5°). Your magnetic heading would be 50.5° (and for a handheld compass clear of metal objects, the deviation will be negligible, so your compass heading will be negligible as well).
To go the other way, for instance if you've taken a compass sight and want to draw it on the map, the rule is:
Chicago Dead Men Vote Twice At Elections
which is:
- take the Compass heading
- adjust for Deviation (again, negligible for a handheld compass in the field)
- gives a Magnetic direction
- adjust for Variation (your 5.5°)
- gives the True direction
- Add East - add if the variation or deviation is East, subtract if it's West
Compass (3°) - (Add East, and the variation is West) Variation (5.5°) = True (-1.5°). This is less than 360°, so add 360° to get 358.5°.
I recommend that newbies get a compass with an adjustable declination[1] (this has become a cheap feature, so a lot of compasses have it), adjust it to the area where they intend to hike, and then work with True directions throughout, changing only when they're hiking outside their home turf. We do well in the field to sight within a degree or two of error, so even the map above will give a reasonable idea of the figure to use. Then, as long as you're using an adjustable compass, there's no worry about getting the arithmetic right, which can be particularly challenging if you're disoriented, the weather is bad, and you're tired - just the conditions you're likely to be under when you're trying to become un-lost. So, for example, living near Albany, New York, I just leave my compass set on 14° West. That' setting is Close Enough for the Adirondacks, the Catskills, and anywhere along the AT from Delaware Water Gap to Maine Junction. I pretty much never hike outside that area at the moment. I'll have to remember to reset it if I ever travel down your way.
The classes that ADK offers teach this method, and for ADK trips in winter or off trail, the participants are required to have an adjustable-declination compass unless they can demonstrate that they're already proficient in another method.
An alternative, that a lot of teachers prefer, is to work in magnetic directions throughout. This is easier if, when you first get a map, you lay it out, take a long straightedge, and scribe lines a couple of inches apart all over it that run magnetic north and south. When you are plotting a direction on the map, you can lay your protractor along one of these lines. Pilots are taught this method, and things like airport runway headings and directions from navigational aids are all quoted as magnetic directions. I like this less well because you have to prepare every map, rather than preparing your compass once.
I'm comfortable with all three methods (adjustable compass, scribed map, arithmetic), but I think the method of using an adjustable compass and working in true directions is the one that I'm least likely to screw up in a bad situation when I'm addled.
= = = = =
[1] I mean an actual compass with a swinging magnet in it. What's the battery life on your compass watch? How repeatable are its measurements? Does its variation change depending on what other functions of the watch are active? And (most important to me) how do you sight it? If all you care is, "is the trail I'm on heading in approximately the right direction," then you don't even need to worry about compass variation. If you're depending on a compass enough to need the variation set, then you need one you can sight accurately.
- take the True direction
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Gah! I thought I understood but still confused...I thought it was obvious that it is East 5.50*, why West? Because the needle is pulled to the west? If East is negative and my declination is negative why isn't it East?mental note wrote:
TJ you explained that perfectly. I always remember it like this "East is least West is best" but acknowledge that that wasn't really your question, (Kelvin nails it in fine fashion and form...beautifully and eloquently text book like) I always have to take a moment too to figure out just exactly what it means in a practical means as well, which is why I like to carry a compass a bone up on map skills in the first place on outings cause that's to only practice I really give myself...which is not nearly enough to my likin'
Good catch on KY!Lost in the right direction. -
There are different kinds of compasses.
When Kathy and I started doing the boundary work along the AT we were instructed to get a quadrant compass.
That's because the maps that we got give heading from one surveyor's monument to the next in quadrant notation.
On that type of compass the face is marked with North and South as 0 and East and West as 90 degrees.
A heading might be,North 15 degrees West. That equates to 350 degrees as you and I know it.
We never bought the compass but just used simple arithmetic to convert and used our regular compass.
We're pretty familiar with where "our" monuments are by now and don't even bring a compass with us. -
Math has always been difficult for me because I want to know WHY you're supposed to do what you do...like there's some philosophical or theoretical guide that if I only understand, I can figure out the answers to problems.
Maybe I'm trying too hard to understand and just need to accept. Lost in the right direction. -
perhaps...music is like that for me, it makes no sense and I just have to to take it for what it is and the rules that govern, kinda like organic chemistry...it is what it is.TrafficJam wrote:
Math has always been difficult for me because I want to know WHY you're supposed to do what you do...like there's some philosophical or theoretical guide that if I only understand, I can figure out the answers to problems.
Maybe I'm trying too hard to understand and just need to accept.
-
Yes, just not the same year. The ship went almost 10 years without a major overhaul in a shipyard. Lots of wear and tear ship board personnel have neither the training nor equipment to make the big repairs with. It didn't help that it was one of the new ships of a class of DDGs. That alone can create problems between the blueprints/ideas and the actual ship.
chief wrote:
Was that the same ship you lost radio communications, 3 of 4 boilers and 1 of 2 turbines and was hit by hurricane Camille?JimBlue wrote:
Another example: our radio navigation went out coming back from the Mediterranean Sea.
--
"What do you mean its sunrise already ?!", me. -
'simple arithmetic'
LIhikers wrote:
There are different kinds of compasses.
When Kathy and I started doing the boundary work along the AT we were instructed to get a quadrant compass.
That's because the maps that we got give heading from one surveyor's monument to the next in quadrant notation.
On that type of compass the face is marked with North and South as 0 and East and West as 90 degrees.
A heading might be,North 15 degrees West. That equates to 350 degrees as you and I know it.
We never bought the compass but just used simple arithmetic to convert and used our regular compass.
We're pretty familiar with where "our" monuments are by now and don't even bring a compass with us.
Also known as mental math...a rapidly vanishing skill.
Lest we forget.....
SSgt Ray Rangel - USAF
SrA Elizabeth Loncki - USAF
PFC Adam Harris - USA
MSgt Eden Pearl - USMC -
Yes, I have to set the declination for my location. I googled the declination for Knoxville and couldn't figure out how to put it in the format that is required on the watch. To tell you exactly what it says will tell everyone where I'm at right now which makes me uncomfortable but this may give you an idea...mental note wrote:
I'm sorry but now I'm confused, does it say in your specs of the watch that it corrects for declination? I can't see how it wouldn't allow for the negative.TrafficJam wrote:
Gah! I thought I understood but still confused...I thought it was obvious that it is East 5.50*, why West? Because the needle is pulled to the west? If East is negative and my declination is negative why isn't it East?Good catch on KY!mental note wrote:
TJ you explained that perfectly. I always remember it like this "East is least West is best" but acknowledge that that wasn't really your question, (Kelvin nails it in fine fashion and form...beautifully and eloquently text book like) I always have to take a moment too to figure out just exactly what it means in a practical means as well, which is why I like to carry a compass a bone up on map skills in the first place on outings cause that's to only practice I really give myself...which is not nearly enough to my likin'
"-5.5 (+E/-W) +-0.##*"
My watch only does positive numbers and one Cardinal.
But I just had an epiphany and see that -5.5 and -W would be the same as W 5.50* because the negatives cancel each other out, right?
Lost in the right direction. -
TJ; Math is a skill based upon real world requirements. Each advancement in mathametics was generated in answer to a need someone recognized. Therefore your need to grasp the 'why' is valid.mental note wrote:
perhaps...music is like that for me, it makes no sense and I just have to to take it for what it is and the rules that govern, kinda like organic chemistry...it is what it is.TrafficJam wrote:
Math has always been difficult for me because I want to know WHY you're supposed to do what you do...like there's some philosophical or theoretical guide that if I only understand, I can figure out the answers to problems.
Maybe I'm trying too hard to understand and just need to accept
I taught a remedial math course for awhile. Several students were able to grasp math concepts when they understood the relationship between music and math.
Lest we forget.....
SSgt Ray Rangel - USAF
SrA Elizabeth Loncki - USAF
PFC Adam Harris - USA
MSgt Eden Pearl - USMC -
I checked Polaris Navigator app on my cell today. Since it goes by gps satelites, being in a car should have no effect. It told me the car was heading North or Northwest when we were actually heading East. So, I'll be uninstalling it.--
"What do you mean its sunrise already ?!", me. -
Declination means "turning."TrafficJam wrote:
Gah! I thought I understood but still confused...I thought it was obvious that it is East 5.50*, why West? Because the needle is pulled to the west? If East is negative and my declination is negative why isn't it East?
West declination == the needle turns to the west, magnetic north is west of true north, or the magnetic pole is west of where you are.
East declination == the needle turns to the east, magnetic north is east of true north, or the magnetic pole is east of where you are.I'm not lost. I know where I am. I'm right here. -
Thank you everyone for not making me feel stupid for my questions. The Cafe is the only place I would ever ask about this stuff.Lost in the right direction.
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