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Real compass vs phone (real compass is bad)

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#1 maxsid

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Posted 06 December 2018 - 04:15 AM

Hi everyone,

So, I was using my phone to find the NCP. Sometimes it was good, sometimes it was bad (Sky Safari).

 

I bought myself a real compass and presumed it would be superior/correct.

To my surprise, the real compass was off by almost 10 degrees to the East. Why? Why??? I re-magnetized it - it didn't help.

 

Interesting thing:

-- I downloaded a compass app for Android - it's also off by the same 10 degrees to the East.

-- Sky Safari (on the same Android device) points exactly at NCP. 

 

WTH?

Thanks!

Max



#2 sg6

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Posted 06 December 2018 - 04:22 AM

Magnetic Declination.

Compass point to the magnetic North, that is different to the polar North.

 

There is a site that gives the difference, will go try and locate.

 

Sunnyvale has a magnetic Declination of 13o 16', so a magnetic compass will indicate just over 13 degrees from true North.

http://www.magnetic-declination.com/

 

I would also half guess that the rocks you are on may add to any magnetic compass, I know that well North of you they are magnetic themselves and really throw a magnetic compass out.

 

I would have thought that a GPS based compass would have shown True North, but I have one on my tablet and it is influenced by anything metallic and magnetic local to it. Oddly the clasp on the tablet case is magnetic and really throws it all.


Edited by sg6, 06 December 2018 - 04:32 AM.


#3 maxsid

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Posted 06 December 2018 - 04:26 AM

Knew about this but didn't think it could be so much of a difference. It's 13 degrees in my area...

Thank you!


Edited by maxsid, 06 December 2018 - 04:31 AM.


#4 penguinx64

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Posted 06 December 2018 - 04:39 AM

I use an Alt/Az mount ,so I don't have to worry about which way North is.



#5 sg6

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Posted 06 December 2018 - 04:51 AM

Yep, if you stick the pin on Sunnyvale it is pretty bad.

 

I was in Sunnyvale for 6 weeks, nice Japanese restaurant in a small retail are up towards the train station. Ate a fair amount in that place. Mind you that was some 16 years ago. Slow train journey to SF. grin.gif grin.gif grin.gif



#6 maxsid

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Posted 06 December 2018 - 05:01 AM

I moved here 17 years ago... Now this place is overcrowded and overpriced.

 

Yep, if you stick the pin on Sunnyvale it is pretty bad.

 

I was in Sunnyvale for 6 weeks, nice Japanese restaurant in a small retail are up towards the train station. Ate a fair amount in that place. Mind you that was some 16 years ago. Slow train journey to SF. grin.gif grin.gif grin.gif


Edited by maxsid, 06 December 2018 - 05:46 PM.


#7 Jim Davis

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Posted 06 December 2018 - 08:51 AM

Phone compasses work the same way as real compasses. There are compass apps that use your GPS location to automatically determine your magnetic declination and correct it for you. There are also GPS apps that will have a true north pointer.



#8 Eddgie

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Posted 06 December 2018 - 09:08 AM

A magnetic compass can be more accurate, but as you have discovered, magnetic declination will give a reading that is different than true north.

The simple solution to this is to either just add or subtract the difference, or get a magnetic compass that lets you adjust in the offset.  Now this will only be good for one area, but if you travel, you can easily re-calibrate the declination.

 

Most good camping and orienteering compasses have the ability to set in declination and I think that these are more accurate than many cell phones. 



#9 eclecto-acoustic

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Posted 06 December 2018 - 09:15 AM

Knew about this but didn't think it could be so much of a difference. It's 13 degrees in my area...

Thank you!

 

It generally gets worse the closer to True North you are. I know that nautical and aviation maps have magnetic declination marked very clearly...not sure what other types deem it important enough.



#10 vtornado

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Posted 06 December 2018 - 01:57 PM

Hello Maxsid, and welcome to cloudy nights.

 

From the electronic devices I have sampled, they use some kind of galvenometer in the device

to find magnetic north.  If the device knows where it is on the globe, most can do the correction for magnetic vs true north.

 

It i my understanding that GPS cannot be used to find direction unless you are moving.

Because it compares coordinates at two different points in time to calculate heading.

 

Of the electronic devices I have tried they are very inaccurate.   I bought a magnetic stand alone digital compass from a reputable firm. I followed the calibration instructions, took it out with no metal on me, or in any direction for 500 ft.   It did not read North when I was facing north, I turned east, south, and west, and back north.  I got varying degrees of error.   I would hate to rely on this thing out in the back country.

 

For those of you gloating about your Alt/az mount.   If you have manual setting circles you do need

to know where North is wink.gif



#11 Jon Isaacs

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Posted 06 December 2018 - 02:37 PM

Of the electronic devices I have tried they are very inaccurate.   I bought a magnetic stand alone digital , from a reputable firm. I followed the calibration instructions, took it out with no metal on me, or in any direction for 500 ft.  

 

One can purchase digital compasses accurate to a degree or so but they are not cheap. The last time I looked, just the sensing unit was several hundred dollars. And they still required calibrations that involved "swinging the compass" (complete revolutions) multiple times.

For what they're designed to smartphone compasses do a good job.For navigating the night sky accurately, not so much.

Jon



#12 vtornado

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Posted 06 December 2018 - 04:27 PM

One can purchase digital compasses accurate to a degree or so but they are not cheap. The last time I looked, just the sensing unit was several hundred dollars. And they still required calibrations that involved "swinging the compass" (complete revolutions) multiple times.

For what they're designed to smartphone compasses do a good job.For navigating the night sky accurately, not so much.

Jon

The compass I was referring too, was not that expensive, probably about $40.00.  It was sold from a hiking store, for use in camping/hiking/fishing etc.  Returned it for full refund.



#13 Migwan

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Posted 06 December 2018 - 08:45 PM

The magnetic north pole is well south of the actual north pole well into Canada.  The only line of declination that would be straight in the states is 0.  As such, everything else curves as you go north, so you need to know your declination and set it on a manual compass.

 

I have used the same compass for 40 years and it has got me out of the woods a number of times here in Michigan on overcast days with no wind.   If it's overcast, I don't go mushrooming with out it. 

 

Doesn't work so well in parts of the upper peninsula round some of the iron deposits there. jd



#14 maxsid

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Posted 07 December 2018 - 01:33 AM

Thank you guys very much - very helpful!


Edited by maxsid, 07 December 2018 - 01:33 AM.


#15 jeffry7

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Posted 07 December 2018 - 11:39 PM

There are compass apps that take your location into account and correct for the local magnetic north, vs. true north.

 

The one I use also includes information about moon rise and set.

 

It is called, unhelpfully, Compass, but you can look for the developer SimplyWerx.

 

https://play.google....pass3d&hl=en_US


Edited by jeffry7, 07 December 2018 - 11:40 PM.


#16 maxsid

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Posted 08 December 2018 - 01:29 AM

This is a good one - thanks!

 

There are compass apps that take your location into account and correct for the local magnetic north, vs. true north.

 

The one I use also includes information about moon rise and set.

 

It is called, unhelpfully, Compass, but you can look for the developer SimplyWerx.

 

https://play.google....pass3d&hl=en_US




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