Okay, You Map-reading Types

[+AuntieWeasel]

I've never really used a magnetic compass until recently, and I'm totally puzzled by its behavior. I've read that you shouldn't get too fussed about buying an expensive one, because they all pretty much work. Well, not for me, they don't.

 

The picture below I took a week ago when I picked up a compass TB, the inset I took today with the compass I carry and a new compass I just bought. I've actually seen them further apart than this (in fact, the picture the closest to accurate I've ever seen two of those compasses get). They're on the kitchen table because the light is good; I get the same kind of results everywhere. Relatively level, letting them "settle" a while. The two in the inset I've let sit next to me on a different table for half an hour, and they're now within thirty degrees of each other. That's terrible!

 

Obviously, if compasses worked this badly all the time, they'd be completely useless. What am I doing wrong? If the answer is that they need to be perfectly level, how will I ever achieve that on a trail?

 

 

I did a cache today where the coords were for a beauty spot, and the actual cache was 150 feet away, ESE. (He only told you this in the hint. Naughty cache hider!). My compass told me it was Due Thisaway, then it said Due Thataway. I reeled all over the cache site like a drunk. I mean, extrapolate 150' using the compass variation in the picture, and you've got a pretty wide arc to search.

 

So how come Lewis and Clark aren't still stumbling around out there in the woods?

[+Stunod]

You seem to have a magnetic personality. That plays havoc with compasses.

[Tahosa and Sons]

Take those compasses outside, keep them separate from each other and see if the bearings are the same. When close together the will attract and repel each other. And there might be metal in your table.

 

Lesson One

 

Lesson Two

 

Lesson Three

 

Final Exam

[+EScout]

Seperate them and place them on something with no steel or iron nearby. I did a similar thing as you and couldn't figure out why they were pointing in different directions. There was a metal support bar under the table I was using.

[+Kfam]

Try holding a magnet north of your compasses. This works on the snazzy buily-in electronic ones of the high dollar GPS units too!

 

You're right though. You really have to have all metal and possibly magnetic things away and hold the thing still and level. Even after the PITA setup, I get similar results.

Maybe that's why they tell you to not waste money on an expensive one.

Have you tried shaking, then averaging readings?

[+NightPilot]

A compass always points north, or to the nearest magnet or chunck of iron. All compasses are magnets. Therefore, compasses close to each other point to each other, or to whatever has a stronger magnetic field.

 

Compasses are influenced by magnetic fields, that's how they work, by aligning with the earth's magnetic field, but if they are in a stronger magnetic field they will align with that field. As others have said, you must be away from magnets, or any mass of iron or other ferric material, like your car or an ammo box, or from electronic gadgets which can emit electromagnetic energy, like your cell phone or GPS.

[+globalgirl]

...you must be away from magnets, or any mass of iron or other ferric material, like your car or an ammo box, or from electronic gadgets which can emit electromagnetic energy, like your cell phone or GPS...

 

Woa! Now hold on just a minute. Noobie here, but still - if you say that electronic gadgets [like your GPS] can play havoc w/ a compass - then how on earth is it that there's a compass IN my gps???

 

I mean, yes, it makes sense that iron, electromagnetic fields and such would decidedly affect a compass. But how is it then, that the compass in a gps (presumably) works accurately???

[+The Puzzler]

if you say that electronic gadgets [like your GPS] can play havoc w/ a compass - then how on earth is it that there's a compass IN my gps???

Two ways:

 

1) A compass can have small (or large) amounts of metal placed around it to stratigically compensate for environmental conditions (how do you think they get compasses to work on steel ships. If you've ever looked at a ship's compass, it will almost surely have had two metal balls on either side of it that were put there and adjusted to compensate for the ships effect on the compass.

 

2) My GPS requires me to "calibrate" the compass by turning in a circle twice, probably so that it can compensate for the difference between a permanant magnetic pull from the GPS electronics and batteries and the variable pull from the earths magnetic field lines as I turn.

[+globalgirl]

Hmmm... most interesting, Puzzler - thanks.

 

Then again...

 

...My GPS requires me to "calibrate" the compass by turning in a circle twice...

 

Are you sure that's not some joke your gps manual is playing on you? LOL, I can just picture you turning in circles each time you turn it on!

 

Ah but seriously, nothing in my gps manual (Magellan SporTrak Map) that talks of calibrating the compass. Wonder why?

[+NightPilot]

Maybe you didn't read the manual completely?

 

The SportrakMap doesn't have a compass. There is a 'compass screen', but that only points in the direction you're *moving*, derived from GPS satellite data, not from any magnetic field. Note that the manual specifically states that you must be moving in order for the pointer to work.

Edited August 15, 2004 by NightPilot

[+globalgirl]

Well yes NightPilot, admittedly I surely have a lot to learn. And yes, I do understand that I need to be moving for the pointer to work. But I thought that was 'cuz it wasn't an "electronic" compass. I didn't realize that it's not a compass at all!

 

Truth is, it's a miracle I've managed to find any caches thus far at all. While I'm surely not stupid, I honestly haven't a clue about navigation, etc. Oh I read most everything I can get my hands on - about the "asmuth" or whatever, etc. But still haven't a clue what half the things do on my gps screen. Like... "Bearing" and "Heading". Though I've googled ad naseum, I'm still unclear just what I'm s'pose to be doing with these/this information.

 

Thanks to All for your patient advice.

[+NightPilot]

Nobody is saying you're stupid. Just a little friendly joshing, and an attempt at an explanation.

 

Azimuth just means direction from here to there. Heading is the direction you're going, and bearing is the direction to the destination. You want to try to make these the same. Sometimes you can't, because of obstacles in the way, but you try to get them back together whenever you can.

 

It will come together with practice. You learn more by doing than by reading, in most cases, but reading and getting an idea of what to do before you try to do it usually helps.

[+globalgirl]

Bless you NightPilot!

...You want to try to make these the same.

 

THAT is what I had finally concluded re: bearing and heading from the reading that I've done. Yet had never found it stated precisely so, and wasn't at all sure if I had it right.

 

Yes, yes - that make perfect sense - ever trying to get them to match (or at least stay close). And I DO halfway understand the numbers - e.g. 270 degrees (i.e. due west, no?), etc. Its just like a compass - trying to line up your path of movement - with the compass point.

 

And YES - no doubt about it. Ever so much better to learn by simply doing (albeit by trial and error oh-so-painfully s-l-o-w-l-y). Unfortunately I don't know any other geocachers, but hope to go to the next local event so will surely learn lots there.

 

Thanks again.

[+AuntieWeasel]

Thanks for the responses (especially the links from Tahosa and Sons. I'm still working my way through them).

 

I take the point about the compasses throwing each other off in the photo. I worked out early on that I could 'push' the needle around with my cellphone. Come to think of it, I used to have a compass in my car that always pointed to the tape player. But I can't seem to get good, consistent readings anywhere in the house. Goodness, are they that sensitive?

 

I'm going to have to go out into a field and 'speriment.

[+briansnat]

Its not totally true that all compasses work the same, no matter how expensive. Junk compasses sometimes don't pivot well, or often develop big bubbles if they are fluid filled. I've also twice encountered ones where the white part of the needle pointed north instead of the red. Thats just poor QC!

 

I'm not saying that you have to shell out $50+ for a compass, but pick out a quality brand like Silva, Brunton or Suunto and plan to spend between $10 and $20.

[gm100guy]

I was helping a guy who got a new gps with a compass built in. It said you had to calibrate by spinning it so many times and some other things.

 

We were in office with a bunch of desk and cabinets and when we tried the compass it was out 180 degrees. We did this operation a bunch of times and still the same.

 

I went out side and tried it and it worked fine, it is best to do not to have metal around.

 

But looking at all your compasses that you have there. Some are hard to use. You should look at one that has the circle over circle, they are easier to learn with.

 

 

The compass I use

 

This also has all the roamers for plotting utm from your gps to a topo map to mark your location.

 

[+EraSeek]

I also use a Brunton Eclipse model, just a bit different. My model . I love it. Compasses also are regionally calibrated and sold in the regions they are meant for. If you have one out of region they will dip too far and scrape the base plate. Just a bit of trivia. This is an interesting thread. Yes you have to be carefull of localized influences, but I'll bet some are just poorly made and align poorly. Also, I've had many compasses and I think every one of them eventually developed a semi-perimate bubble from taking it up 10,000'. Of course the most expensive I've own was about $40.

 

Read this about the Global Needle

Edited August 15, 2004 by EraSeek

[+mogle1]

My 2cents worth.

I have been a land surveyor for almost 30 years now and have used many different kinds of compasses over that period of time ranging from cheap little dime store to suunto to the ones that come in the old K&E mountain transits and some of the older theodolites Brunton, Wild, Dietzgen. I don't think any of them ever pointed exactly the same direction. Of course the upper end theodolites were within less than a minute each other.

With the hand held compasses it doesn't take much to throw them off. Overhead powerlines, car parked nearby ( had one 20' away that threw me off 10º), car keys, pocket knife, etc. To get a real good reading you should have nothing metalic on your person and be as far away from large metal objects and power lines.

[+archeangelsk2002]

the compass in general can be a valuable navigation tool. this is especially true if you no longer have access to batteries for your GPSr. for specific training and info on the use of a compass i recommend this book

BASIC ESSENTIALS

MAP AND COMPASS 2nd. Ed

by: Cliff Jacobson

 

regards

archie

[4x4van]

Since you have the SporTrak Map, I thought I'd add a quick and easy hint for you. All Magellan GPS units have what's called the "Northfinder" feature. Look at the "compass screen" on your GPS. There will be an icon for the sun and/or moon somewhere around the outside of the compass rose. Line that icon up with the sun/moon in the sky, and the compass rose is now oriented correctly. I found the easiest way is to directly face my shadow, and then rotate the GPS so that the sun icon is facing me. At night, I will face the moon and rotate the GPS so that the moon icon is opposite me on the screen. Keep in mind this is only necessary when standing still, since once you start moving, the compass rose will orient itself correctly anyway. (Remember also, if you are going to compare it to a handheld compass, set your GPS to "Magnetic North" as opposed to "True North".)

 

I carry a decent Brunton compass, as well as a smaller "ball" style that's clipped onto my right shoulder strap for quick and easy viewing, but by using the "Northfinder" feature, I've yet to actually need either.

Edited August 16, 2004 by 4x4van

[+mr_and_mrs_mo]

So then, as another newbie, does all of this mean that perhaps the gps with the compass is not so necessary? Looking at the price difference between the ones with and the ones without, perhaps I should get one without and spend $10-$20 on a sep. compass?

[+briansnat]

So then, as another newbie, does all of this mean that perhaps the gps with the compass is not so necessary? Looking at the price difference between the ones with and the ones without, perhaps I should get one without and spend $10-$20 on a sep. compass?

Yes, since models with an electric compass cost anywhere between $50 and $150 more than similar ones without, you can save money by buying a inexpensive hand held compass. Now if money is no object, the electronic compass on your GPS is a very nice feature to have.

[+NightPilot]

IMO you're better off with a real magnetic compass than the one in the GPS, or at least get a magnetic compass in addition to the GPS. Magnetic compasses don't need batteries, they work when wet, don't care about the temperature, you just have to keep ferrous metal and RF emitters away from them. I would never spend the money on a GPS with an electronic compass, but then I'm cheap.

[+EraSeek]

IMO you're better off with a real magnetic compass than the one in the GPS, or at least get a magnetic compass in addition to the GPS. Magnetic compasses don't need batteries, they work when wet, don't care about the temperature, you just have to keep ferrous metal and RF emitters away from them. I would never spend the money on a GPS with an electronic compass, but then I'm cheap.

-ditto-

[+JohnnyVegas]

Get a copy of a book called "the Basic Essentials of Map and Compass" this is a very good book for some one just getting started in the use of a map and compass, you should also have a map of the area you will be in.

[+globalgirl]

...Line that icon up with the sun/moon in the sky...Keep in mind this is only necessary when standing still, since once you start moving, the compass rose will orient itself correctly anyway.

 

Woa, thanks 4x4van - that's a great tip! Will give it a try, thanks!

[4x4van]

Yup, it's a great feature that even the older Magellans have. My first GPS was a Magellan GPS315, and it had the Northfinder. I now use a SporTrak Pro which also has it. When I recently picked up an ETrex for my son, I was surprised that the Garmin units don't have it. Even though it doesn't replace an actual compass, once you use it a few times, it becomes worth it's weight in gold. I can't figure out why Garmin doesn't add the feature to their units, unless Magellan has some sort of a patent on it or something.

 

As I said, with the Northfinder, I've yet to need to use a compass, even though I do carry a couple just to be safe. Never know when your batteries are going to take a dump!

[+EraSeek]

Northfinder. I was surprised that the Garmin units don't have it. I can't figure out why Garmin doesn't add the feature to their units, unless Magellan has some sort of a patent on it or something.

 

Garmin has the same thing, they just don't make anything of it. Select "celestial" , and the select sun/moon rise/set page and use the graphics to line up with the sun or moon, and the unit is pointing North.

[+Sputnik 57]

At night, I will face the moon and rotate the GPS so that the moon icon is opposite me on the screen.

At night I face Polaris, which gets me within a degree of true (not magnetic) north. But then again, what do you expect from someone used to being in orbit.

 

--Sput

[+Zen Cooker #1]

I skimmed through the lengthy thread so this may have been covered...

 

Get a USGS topo map of where you live and find a road that points directly north/south. Go there and take a reading down the centerline (away from any metal, of course). That will tell you what is accurate and what isn't, and it's easier than using the sun icon, North Star, etc.

 

This is very important: your compass needle will most probably not point to true north (star or pole) . It probably won't point to magnetic north either. => The compass needle aligns with the earth's magnetic field at your location <= The angle from true (map) north is called the deviation and must be taken into account to get accurate readings. Where I live in New Mexico, the deviation is 10.5 deg. east, i.e., the compass needle points 10.5 degs. east of true north. When the needle points there and is aligned with the compass index marks, I'm looking straight north. True north.

 

Get a magnetic compass that has fluid damping and adjustable declination setting, set the declination to the angle shown on the bottom of the topo map, check it out on the road, and you're done -- forever.

[+imfishinohio]

I'm new too and this was a good thread and might keep me from making some mistakes. Zen them are some good hints which I think I will try on my compass.

Edited August 18, 2004 by imfishinohio

[4x4van]

Northfinder.  I was surprised that the Garmin units don't have it.  I can't figure out why Garmin doesn't add the feature to their units, unless Magellan has some sort of a patent on it or something.

 

Garmin has the same thing, they just don't make anything of it. Select "celestial" , and the select sun/moon rise/set page and use the graphics to line up with the sun or moon, and the unit is pointing North.

Interesting. Do you know which Garmin models have that? My son's yellow ETrex has sunrise/set times, but not sun/moon position. In any case, the nice thing with the Magellan is that you don't have to go to yet another screen to access it. The icons are always on the compass screen, which is the screen I use most of time when I get near ground zero, anyway. Of course I can also go to another screen to get exact sunrise/sunset, moonrise/moonset times and moon phases, along with the "supposedly" best times for hunting and fishing.

Edited August 18, 2004 by 4x4van

[+EraSeek]

On my Map76 it is all on the same page, times of sun/moon set/rise and graphics showing where they currently are in the sky. The celestial menu option also includes tides which are also graphed out showing where you are time wise in the graphed tides, and selectable location ability to find tides where ever you wish, and it also has hunting/fishing times which I never use.