Compass Calibration Question

[knowschad]

I have one friend that simply spins his Garmin on its axis while holding it horozontal. I have another that insists that he gets better accuraccy by holding it at arm's length while turning his body on axis. Which one is right, or does it even matter?

[+RonFisk]

I have one friend that simply spins his Garmin on its axis while holding it horozontal. I have another that insists that he gets better accuraccy by holding it at arm's length while turning his body on axis. Which one is right, or does it even matter?

I really don't think it makes any difference as long as it turns at least 720 degrees in one direction while being held level.

[knowschad]

I have one friend that simply spins his Garmin on its axis while holding it horozontal. I have another that insists that he gets better accuraccy by holding it at arm's length while turning his body on axis. Which one is right, or does it even matter?

I really don't think it makes any difference as long as it turns at least 720 degrees in one direction while being held level.

 

Thanks, but I guess I should have stated that I'm looking for factual information, not speculation. I know we've got some people here with in-depth knowledge of how these things work... that's the sort of answer that I'm looking for.

[+Team Chinook]

Whilst fiddling with the Colorado 400T at REI this past week I calibrated the compass per the on screen instructions - hold flat in your hand and rotate twice in one direction.

 

Ciao!

 

I have one friend that simply spins his Garmin on its axis while holding it horozontal. I have another that insists that he gets better accuraccy by holding it at arm's length while turning his body on axis. Which one is right, or does it even matter?

I really don't think it makes any difference as long as it turns at least 720 degrees in one direction while being held level.

 

Thanks, but I guess I should have stated that I'm looking for factual information, not speculation. I know we've got some people here with in-depth knowledge of how these things work... that's the sort of answer that I'm looking for.

[knowschad]

Whilst fiddling with the Colorado 400T at REI this past week I calibrated the compass per the on screen instructions - hold flat in your hand and rotate twice in one direction.

 

Rotate the Colorado, or rotate your body? That's my point. I guess my question is more along the lines of "how does compass calibration work?" Is there any advantage (or disadvantage) to having it swing a large circle?

 

Again, I don't mean to be rude, but I'm looking for knowledgable answers... I am quite capable of making my own educated guesses. Looking for fact, not opinion.

[+twolpert]

The important thing is to hold the unit as level as possible while turning through two full revolutions in the same direction. The Colorado has a two-axis compass (as opposed to three-axis), which means that holding it absolutely level is important. This is easier to do by turning your body than it is by turning the unit in your hand. I suspect that is the reason behind any "improvement" you might see when turning your body.

 

I am, however, curious as to how anyone can tell how "well-calibrated" the unit is. It's obvious when it's not calibrated at all. But the only way I can imagine testing the calibration is to compare the unit to an ordinary compass. Not sure anybody is motivated enough to do that?

[jholly]

First off it is very important to hold it at least an arms length away. Slowly walk in a small circle. It is very important to click your heels together once when you first start, twice after the first circle and three times an the end. Make sure your not near any cars, power lines, radio antennas, strong magnets, or lodestone deposits. The whole time your doing this you need to repeat the words "I can calibrate my compass".

 

Jim

[+Team Chinook]

www.garmin.com/manuals/eTrexVista_QuickReferenceGuide.pdf

 

From Garmin - no conjecture, opinion, nor wild-a** presumptions. Good enough?

 

Googled, "garmin compass calibration" and it was the fourth item to show up. Try it some time g-o-o-g-l-e

[knowschad]

www.garmin.com/manuals/eTrexVista_QuickReferenceGuide.pdf

 

From Garmin - no conjecture, opinion, nor wild-a** presumptions. Good enough?

 

Googled, "garmin compass calibration" and it was the fourth item to show up. Try it some time g-o-o-g-l-e

 

Thanks for the sarcasm to a serious question, TC. Why did you feel the need to post that?

 

The Garmin documentation you referenced SPOKE about turning the body, but showed a picture of turning the unit. I did not ask HOW to calibrate... I asked what is the best method. And yes, I do know how to use Google quite well, thank you.

[Hertzog]

I think I like jholly's approach the best

 

Seriously, it doesn't really matter HOW you rotate it, just that you rotate it twice, holding it level, and at a continuous moderate speed. About all that can really be "calibrated" are the output amplitudes of the two sensors (probably offsets, and possibly relative magnitudes - Garmin won't tell us what they do, and I haven't seen any indications in the many past threads on this subject that anyone has delved into it).

 

The unit will tell you if you are holding it level and turning at the right rate, so when your friend is holding it at arms length he will not be able to get that feedback. However, once you have the "feel" for those things you don't need to refer to them continuously, and it occurs to me that holding it at arm's length might help to keep it level; the next time I calibrate I'll try that out. Bottom line, if you find an approach that you feel works for you, use it.

[Skippermark]

This is a guess and not exactly what you're looking for, but if you spin your body versus the unit itself, you're spinning around a "looser" axis than if you spin the unit itself, causing the unit not to have a great center point. I'm kind of visualizing a top spinning tightly on the little point versus someone holding a top and spinning their body.

[Glenn W]

The following are instructions for a CORSA handheld compass which uses a fluxgate sensor similiar to the Garmin. It recommends turning your body in circles but stresses that the size of the circles makes no difference.

 

"Holding your Corsa Digital Compass

level, slowly turn around in complete two

circles and then press ENT. Each circleshould take

a minimum of four seconds.

 

The compass heading should be displayed.

You have calibrated your compass. Enjoy!

NOTE: The size of the circles or the

direction the Corsa Digital Compass is

pointing when beginning or ending the

circles does not matter. The circles do

not have to be perfect circles. The most

important factors during calibration

are that the Corsa Digital Compass is

held level, more than one and a half

circles are made, and is completed in

less than 2 minutes."

[knowschad]

The following are instructions for a CORSA handheld compass which uses a fluxgate sensor similiar to the Garmin. It recommends turning your body in circles but stresses that the size of the circles makes no difference.

 

 

Perfect! That's exactly the sort of answer I was hoping for. Thanks much.

 

(PS: and here I always thought that flux-gate sensors sent you back to the future!)

[Hertzog]

...it occurs to me that holding it at arm's length might help to keep it level; the next time I calibrate I'll try that out. Bottom line, if you find an approach that you feel works for you, use it.

I tried the "extended arm" approach today, and I have to say that it seems to work for me. Over the past 7 years or so I've attempted to get good calibrations on three different GPSrs (Vista, 60CS and 60CSx) and have never ever been really happy with the results; I've always been left with about a 5 to 10 degree error, but never could figure whether it was the GPSr, my calibration technique, or my sighting technique. After just the one extended arm calibration the maps nicely align to the real world now in the "track up" mode (they have always been clearly rotated before), and sightings taken along roads clearly line up with the roads (usually they are about 5 to 10 degrees off). Haven't tried sighting any distant objects yet, but I would expect similar results. I would say I am now getting within 1 degree, 2 at the outside.

 

Could be just a one-time fluke of course, but it IS the first time in about 7 years that I can remember getting readings that I really like. I'm thinking that extending the arm may be getting the GPSr away from metallic objects on the body (belt buckles, knives, cameras etc.) that could distort the local magnetic field and introduce errors in the calibration. I've always been aware of these possible effects and tried to minimize them, but if you are holding it in your hand close to your body and either turning it in your hand or spinning yourself, there is only so much you can do. I'll continue to use this "extended arm" approach as long as I get good results. Thanks to the OP for bringing it up.