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Magnetic Vs. True Readings On Gps


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So here we are - we've been caching for almost a year...at 88 finds, and I feel like a newbie asking this question. Today we found a cache that gave a bearing in true degrees. No problem, took the little yellow eTrex and switched it over to true compass readings. Just now, I was going to switch it back, and then I stopped. Should I? Does the bearing matter all the time? Will I not be able to find caches with the compass set to true instead of magnetic? Guess it sounds like I need a brief lesson in GPS compass settings...

 

~Jared

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The arrow will point to the cache whichever mode you're in.

 

The magnetic vs. true setting only matters when you're actually taking or using bearings. We used to carry a magnetic compass with our GPS, so it was always set to magnetic - that way the numbers line up with each other.

 

You may as well leave the setting until you need to switch it for another bearing in the future.

 

Cheers,

 

Stu

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The arrow will point to the cache whichever mode you're in.

 

The magnetic vs. true setting only matters when you're actually taking or using bearings. We used to carry a magnetic compass with our GPS, so it was always set to magnetic - that way the numbers line up with each other.

 

You may as well leave the setting until you need to switch it for another bearing in the future.

 

Cheers,

 

Stu

Good answers. It all depends on what you are doing. I leave mine set to magnetic so I can take a bearing off of a paper map with my protractor without having to adjust for declination. Then I can just enter the bearing into the GPS. I use true if the cache page tells me to otherwise its always in Magnetic.

 

 

Now just forget all that I just said and listen to stu_and_sarah. They have it simple and correct. Everything I posted is true but if you are never going to use a paper map and a protractor (and why should you, you have a GPS) you wont need it. Old habits die hard. :(

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Huh? Paper maps are aleigned to TRUE north. At any rate, I always use TRUE. I have a compass with an adjustable declination, so that also points me to true. If you have a compass that does not adjust, it is quite easy to off set your bearing by so much for your declination anyway. No prob. Never the less, they are right. It matters little which you use, as long as your GPS and compass are on the same page. Easy to do either way. Your GPS will either need to adjust itself to MAGNETIC, or you need to adjust your comapss reading to TRUE. I like TRUE because it point to the north pole, not to a spot in northern Canada.

 

HERE is a link to find your declination. OR you can just set your GPS to magnetic and most will tell you how much it is offset to match the declination.

 

Go to the page, select compute declination (you may have to select Declination (not programs) and then select compute declination), put in your zip code or coords, and hit compute.

Edited by EraSeek
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The nice thing about Illinois is that the declination is practically nil. I have been in other areas where the declination is more severe and it's always a challenge for me to adjust my head accordingly. :(

 

I leave it on true north, but I would guess that since I do a lot of work with a standard magnetic compass, for convenience sake I'd switch to magnetic north if it made that much of a difference.

 

Bret

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Buy an inexpensive magnetic compass and set the GPS to the same. Now you can use the compass as an extra help when you get in proximity of the cache, and if you lose it, at least it was inexpensive...

 

Remember, almost all GPS will only show your heading when you are 'moving'; although they will show the bearing regardless. This is when a compass is handy.

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I agree with EraSeek in setting everything to True. Many compasses have a decllination adjustment. Those that don't, put a mark at the declination on the bottom of the inner part of the compass, and line the needle over this-- very simple.

The setting of true or magnetic in your GPSr is used when you read bearings to a waypoint, bearings between points in a route, and for projections from a waypoint or your location. My three multi-caches use all of these, and I specify which reference to use.

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I like TRUE because it point to the north pole, not to a spot in northern Canada.

You forgot to add "..... a spot in northern Canada FOR NOW"

Magnetic north shifts around from time to time. It has been quite a long time since the north pole changed.

 

(:

Yup! Quite true. Mag north will be in Siberia in 2050.

 

nmppath2001.gif

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J & T if you can find this Cache you will know how to use one of those magnetic marvels before the day is over.

 

I always use magnetic and do the "East is Least, and the Truth is Greater" when using UTM grid orientated map. One needs to know the difference between a map bearing and a field bearing. And how to adjust for declination, even though I have several adjutable compass I still prefer the old fashioned way. Stick it to a refrigerator.

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:blink: Brain fuzzelage and smoke streaming from ears and eyes all crossed. The answers every one gave are all fine. But to keep it simple and understandable,you really have to know about using a compass and paper maps. Since paper maps are oriented to "True North", (meaning that if you placed a paper map on the table you want to know which way to turn the map to put the top of the map facing North) The up and down grid lines on a map are oriented to True North, not magnetic north, so when you place your compass on the map and the needle points to north it is pointing to magnetic north, not true north. So you look at the bottom of the map and it will tell you how many degrees difference there is between magnetic and true north, then you can turn your map so that it points to true north, which is in line with the grid lines. Hope this helps! .........PS: GPS units, in there defalt mode, use Magnetic North. You really don't need to change over unless you are dealing with a paper map or the CACHE is given in true north readings. Edited by Southview
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My compass always reads true north......when the needle is over the declination mark (13.5° E here locally)

Once again; for compasses with a declination adjustment: set it and forget it.

For compasses without the adustment, there is usually a declination scale. Put a black mark there and line the needle over it. The azimuth ring will read true north.

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Magnetic or True. Another point to consider, many road grids are on true, if the GPSr is also set to true, when the goto arrow points north (or east/west/south) you can use the road grid to navigate. Doesn't help as much here where roads twist and turn around the hills, but the concept is good.

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