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True or magnetic north?

#1 User is offline   airhogs123 

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Posted 07 August 2009 - 03:51 PM

I was just wondering which setting would be better for my GPSmap 60CSx true or magnetic north? I have noticed when searching for caches the compass can bounce around even when not under any cover. I have it set to true north.

#2 User is offline   Tequila 

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Posted 07 August 2009 - 03:54 PM

When navigating to a lat/long, it does not matter. It is only important when projecting a waypoint.

#3 User is offline   ThomThom43 

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Posted 07 August 2009 - 03:58 PM

View PostTequila, on Aug 7 2009, 03:54 PM, said:

When navigating to a lat/long, it does not matter. It is only important when projecting a waypoint.


If you are checking the location of your target with a hand held compass, the setting is extremely important.

#4 User is offline   RonFisk 

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Posted 07 August 2009 - 06:13 PM

View PostThomThom43, on Aug 7 2009, 04:58 PM, said:

View PostTequila, on Aug 7 2009, 03:54 PM, said:

When navigating to a lat/long, it does not matter. It is only important when projecting a waypoint.


If you are checking the location of your target with a hand held compass, the setting is extremely important.


I have mine set for True. But it's a matter of personal preference. If working with a compass (which I rarely ever do anymore) I'd set it for Mag.
The setting has nothing to do with bounce. It'll be the same either way.

This post has been edited by RonFisk: 07 August 2009 - 06:15 PM


#5 User is offline   airhogs123 

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Posted 07 August 2009 - 06:32 PM

What could be the reason the compass seems to bounce all over the place?

#6 User is offline   BlueDeuce 

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Posted 07 August 2009 - 07:06 PM

View Postairhogs123, on Aug 7 2009, 09:32 PM, said:

What could be the reason the compass seems to bounce all over the place?


You need to recalibrate the compass after every battery change.

#7 User is offline   Team Veverca 

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Posted 08 August 2009 - 02:50 AM

View PostBlueDeuce, on Aug 8 2009, 05:06 AM, said:

View Postairhogs123, on Aug 7 2009, 09:32 PM, said:

What could be the reason the compass seems to bounce all over the place?


You need to recalibrate the compass after every battery change.

And don't carry your GPS in a bag that has a magnet to close it. I used a bag from my old SE p910 and the compass gave me a lot of trouble. Then I noticed that it's because of the magnet that was ment to close the bag. It messed with my compass.

#8 User is offline   airhogs123 

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Posted 08 August 2009 - 07:15 PM

I will try that.
Thanks!

#9 User is offline   dostuffgps 

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Posted 08 August 2009 - 08:05 PM

I have wondered the same thing and I'm glad someone asked this question.

#10 User is offline   airhogs123 

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Posted 10 August 2009 - 11:35 AM

Any more helpful hints or tips I can try?
Thanks airhogs123

#11 User is offline   John E Cache 

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Posted 10 August 2009 - 01:46 PM

Look at the bearing and distance and lat/lon when you are near a cache and standing still. All those numbers bounce because your location changes by as much as 30 feet between the periodic measurements. Everyone picks on the compass because it is the most visible. If your location bounces to the other side of the cache, of course the compass will swing 180 degrees. The arrow is the current best guess at a bearing to the cache. Try following the arrow when it bounces and I do mean the arrow(the arrow points at the cache location guess even if you rotate the GPS).

This post has been edited by John E Cache: 10 August 2009 - 01:54 PM


#12 User is offline   ecanderson 

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Posted 11 August 2009 - 07:18 AM

View PostBlueDeuce, on Aug 7 2009, 09:06 PM, said:

View Postairhogs123, on Aug 7 2009, 09:32 PM, said:

What could be the reason the compass seems to bounce all over the place?


You need to recalibrate the compass after every battery change.
That would be a bit too late, although also necessary. For some reason, Garmin's design of the mag compass is heavily dependent upon the battery voltage. I find it necessary to recalibrate not only when installing fresh batteries, but once or twice as I burn them down as well. Typically, I'll recal when I see the first bar disappear from the battery indicator, then again as the second disappears if I haven't changed them already.

I wish they'd come up with an internal regulator for the compass to prevent its accuracy from being so voltage variable. DC/DC regulation has become pretty efficient over the years.

#13 User is offline   DeadHead82 

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Posted 11 August 2009 - 08:12 AM

I'm starting to wonder about the compass bounce issue. I've used a 60csx that I received as a birthday gift (i know, spoiled!) for about a year now, and have never once observed the compass going goofy. I've always recalibrated upon battery changes, and that's all i've had to do. I've even tested it, under different conditions against my suunto M3 and it's been just fine. The only time i've seen the compass bouncing around is when i'm close enough to a cache to cause drastic changes in bearings due to the units measurements. At that point it's time to put the GPSr away and start searching anyway. When navigating to a waypoint (cache or otherwise, since my usage of the unit is only about 10% caching) i leave the compass turned off so i can hold the unit upright to look at it, using my heading for direction. When i see it's time to break off of the trail, I stop, hold the unit flat, turn the compass on, shoot a bearing, and head in that direction. I've only found around 40 caches so far, but I've used this procedure many times, and have always ended up very close to where i needed to be. I've seen so many threads about this i even used the units compass, as well as my "old fashioned" one to navigate to a point from a set location and have received similar results. The bearings between the two were not exact, but close enough to get me in the general vicinity of the Lat/Lon i was shooting for. The error in bearings between the two can be attributed to EPE of the GPSr. I guess maybe i'm just lucky or something. It's a total bummer so many people are seeing this issue, because i really believe my 60 is an awesome unit and would recommend it to anyone. However, there may be some bias there, as it is the only unit i've ever used. One of my best buddies from waay back had an old explorist 200 but i've only seen him use it, never used it myself.

#14 User is offline   twolpert 

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Posted 11 August 2009 - 08:41 AM

View PostJohn E Cache, on Aug 10 2009, 04:46 PM, said:

Look at the bearing and distance and lat/lon when you are near a cache and standing still. All those numbers bounce because your location changes by as much as 30 feet between the periodic measurements. Everyone picks on the compass because it is the most visible. If your location bounces to the other side of the cache, of course the compass will swing 180 degrees. The arrow is the current best guess at a bearing to the cache. Try following the arrow when it bounces and I do mean the arrow(the arrow points at the cache location guess even if you rotate the GPS).

This is exactly the issue. It's mostly due to multi-path effects. Units from different manufacturers (and even different models from the same manufacturer) do a better/worse job of damping out multi-path effects. If the unit does it badly, you have obvious problems due to abrupt shifts in reported position which may put you on different sides of the cache. In addition, some units may suffer from problems due to shifting back and forth between compass and satellite data for direction of travel. If the speed of the apparent position shift is high enough, the unit may momentarily shift to satellite data for direction of travel. This causes the "arrow" to swing in yet another direction, further confusing the poor cacher standing still on the ground. The fundamental issue is not the compass -- it's failure to properly damp multi-path artifacts.

#15 User is offline   twolpert 

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Posted 11 August 2009 - 08:44 AM

View Postecanderson, on Aug 11 2009, 10:18 AM, said:

I wish they'd come up with an internal regulator for the compass to prevent its accuracy from being so voltage variable. DC/DC regulation has become pretty efficient over the years.

This may not be a voltage issue. It may instead be related to magnetic fields generated within the device. Amounts to the same issue, though. I wonder if others are having the same type of problem with this model, of if you might have a somewhat defective unit?

#16 User is offline   vickiandsteve.com 

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Posted 18 April 2010 - 10:13 AM

So should I set the setting to "magnetic north" or to "true north" for geocaching? GPS is a Garmin eTrex Vista Cx. Thanks.

#17 User is offline   ecanderson 

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Posted 18 April 2010 - 11:34 AM

View Posttwolpert, on Aug 11 2009, 10:44 AM, said:

View Postecanderson, on Aug 11 2009, 10:18 AM, said:

I wish they'd come up with an internal regulator for the compass to prevent its accuracy from being so voltage variable. DC/DC regulation has become pretty efficient over the years.

This may not be a voltage issue. It may instead be related to magnetic fields generated within the device. Amounts to the same issue, though. I wonder if others are having the same type of problem with this model, of if you might have a somewhat defective unit?
Naw - it's voltage. If you want a few (not) grins, fire one up with the compass enabled and drive it with an external supply across a range of 2.4V to 3.5V. Watch where the compass goes. It's why the compass begins to whack out as the batteries become a bit depleted, and why if you calibrate at that lower voltage point, it whacks out again when you install fresh ones.

#18 User is offline   ecanderson 

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Posted 18 April 2010 - 11:38 AM

View Postsreigle, on Apr 18 2010, 12:13 PM, said:

So should I set the setting to "magnetic north" or to "true north" for geocaching? GPS is a Garmin eTrex Vista Cx. Thanks.
Since you will be using the compass (usually) to derive a bearing to the target vs. how you're holding your GPSr, and since the coordinate grid for WGS84 uses true north, you'll want to stick with "True", especially if the declination in your area is severe and would throw "North" off by a bunch.

#19 User is offline   Walts Hunting 

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Posted 18 April 2010 - 03:17 PM

If you tell your GPS to take you to some location the true/magnetic is irrelevant. The only difference it will make is the degrees it shows as the bearing. The arrow will point to the target regardless.

That being said the world generally operates in True North. The only time you will need the magnetic is if some local evil cacher decides to make you do a multi using magnetic so you have to the change the settings. This same evil person also might give the second stage coordinates in UTM so brush up on that.

#20 User is offline   ecanderson 

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Posted 18 April 2010 - 08:44 PM

View PostWalts Hunting, on Apr 18 2010, 05:17 PM, said:

If you tell your GPS to take you to some location the true/magnetic is irrelevant. The only difference it will make is the degrees it shows as the bearing. The arrow will point to the target regardless.
Any of the units with a magnetic compass will, while you are standing still, make assumptions about north and how the unit is being held in your hand. WGS84 assumes true north. So if you set the compass to "magnetic", the arrow will be missing the target bearing by the amount of the declination error. The farther you are away from the cache, the worse the error as you survey the terrain.

Stick with "true" if you own a unit with a mag compass and actually use it.

This post has been edited by ecanderson: 18 April 2010 - 08:45 PM


#21 User is offline   vickiandsteve.com 

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Posted 01 April 2013 - 06:06 PM

Thanks for several very helpful replies. Appreciate it.

#22 User is offline   yogazoo 

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Posted 01 April 2013 - 06:34 PM

It's my understanding that it really doesn't matter what your GPS compass is set to (true or magnetic) unless you plan on using a paper map in conjunction with the compass on your GPS OR if someone gives you a bearing depending on their setting (whether or not their dedicated compass is adjusted for declination).

If you are navigating to a waypoint the GPS unit knows where that waypoint is regardless of the setting. It's just like the coordinate system in your GPS unit. It's only important if receiving information from or relaying information to a separate entity. The GPS automatically adjusts when navigating. It won't point you in the wrong direction either way providing the compass is properly calibrated.

I pretty much reiterated what everyone here has been saying. But I have a question for anyone, is there an advantage to manually checking a bearing from a digital device?

This post has been edited by yogazoo: 01 April 2013 - 06:49 PM


#23 User is offline   7rxc 

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Posted 03 April 2013 - 07:34 AM

View Postyogazoo, on 01 April 2013 - 06:34 PM, said:

It's my understanding that it really doesn't matter what your GPS compass is set to (true or magnetic) unless you plan on using a paper map in conjunction with the compass on your GPS OR if someone gives you a bearing depending on their setting (whether or not their dedicated compass is adjusted for declination).

If you are navigating to a waypoint the GPS unit knows where that waypoint is regardless of the setting. It's just like the coordinate system in your GPS unit. It's only important if receiving information from or relaying information to a separate entity. The GPS automatically adjusts when navigating. It won't point you in the wrong direction either way providing the compass is properly calibrated.

I pretty much reiterated what everyone here has been saying. But I have a question for anyone, is there an advantage to manually checking a bearing from a digital device?


Such things do matter to some people some times under some circumstances. When dealing with short distances, the difference between bearings is small, be it Magnetic N, True N or Grid N. The real trick is to know when to worry about it. Personally, I do what is needed to reference True North on all devices, most of the time. I use a handheld (declination adjustable) compass that is not part of a GPS... If I need to reference it, the important thing is that it 'zeros' the same as the GPS. And in answer to the last question any time precise navigation is needed, one should always cross reference bearings to avoid error creeping in, never one source.

Doug 7rxc

#24 User is offline   New Jersey TJ 

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Posted 08 April 2013 - 09:34 PM

View Postecanderson, on 18 April 2010 - 08:44 PM, said:

View PostWalts Hunting, on Apr 18 2010, 05:17 PM, said:

If you tell your GPS to take you to some location the true/magnetic is irrelevant. The only difference it will make is the degrees it shows as the bearing. The arrow will point to the target regardless.
Any of the units with a magnetic compass will, while you are standing still, make assumptions about north and how the unit is being held in your hand. WGS84 assumes true north. So if you set the compass to "magnetic", the arrow will be missing the target bearing by the amount of the declination error. The farther you are away from the cache, the worse the error as you survey the terrain.

Stick with "true" if you own a unit with a mag compass and actually use it.


I think I'm with Walt's Hunting on this one. The arrow will always point to the target, regardless of the true/magnetic setting. The true/magnetic setting really just adjusts where North is (or which North you're using, so to speak). Since walking to a cache just involves a bearing, that setting won't really matter, the arrow will still point to the cache. The azimuth that you're walking may be off by the declination, but unless you're trying to plot on a paper map, that's of no significance.

This post has been edited by New Jersey TJ: 08 April 2013 - 09:36 PM


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