/ Digital Compass

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FesteringSore - on 17 Jul 2017
I loaded a digital compass app on to my phone. I was quite amazed at how inaccurate they can be when compared with a standard magnetic (Silva) compass. Despite following the instructions for calibration there is, at times, a discrepancy of up to 60 or 70 degrees.
No substitute for the real thing!
Crewey-Rob on 17 Jul 2017
In reply to FesteringSore:

It's annoying because they look good, I have one (GPS Status) that wouldn't look out of place in the cockpit of a stealth bomber but it is 20 degrees out so not too accurate (it's a toy I suppose)
FesteringSore - on 17 Jul 2017
In reply to Crewey-Rob:
Yes, mine looks very business like but I do wonder if they should come with a warning about reliability. I take it no self respecting walker/climber etc is going to use one at the expense of a trusty magnetic one.
I suppose I had it in mind to use it as some sort of stand-by but I see little point in that.
Post edited at 16:54
Lusk - on 17 Jul 2017
In reply to FesteringSore:
> ... there is, at times, a discrepancy of up to 60 or 70 degrees.

That's the difference between getting off the top of Ben Nevis in the mist/whiteout and wandering off the edge of the north face (which I would've done once if hadn't put faith in my compass reading).

> No substitute for the real thing!
Indeed.
Post edited at 16:59
tom_in_edinburgh - on 17 Jul 2017
In reply to FesteringSore:

> I loaded a digital compass app on to my phone. I was quite amazed at how inaccurate they can be when compared with a standard magnetic (Silva) compass. Despite following the instructions for calibration there is, at times, a discrepancy of up to 60 or 70 degrees.

How did you test the phone compass against the Silva compass?

If you had the Silva compass near the phone when you compared them the magnets in the phone speakers would affect it but (hopefully!) the phone's digital compass would be calibrated to compensate for them.

I guess the digital compass in a phone is mainly to give GPS a hint about which way you are facing so as to orient the map display and there's not much reason to put effort in to make it super accurate. Not many people are going to want to take bearings when they have a GPS.




Jack B on 17 Jul 2017
In reply to FesteringSore:

Barring some fairly extreme incompetence on the app-writer's part, the app will be as accurate or inaccurate as the magnetometer in the phone. The one in my S4 is actually pretty good, limited by the lack of sighting aids rather than the magnetometer. Except I use a flip cover with magnets in so it's worthless unless I take the back off the phone.

It's worth noting that the GPS chip in the phone can almost certainly provide "course made good" which will be a very accurate measurement of the direction you are moving in. It is much more accurate than you would get by taking successive positions, with uncertainties, and working it out. If you can find an app which makes good use of that, then it is fine to use for navigation. Speed made good is also reported.
captain paranoia - on 17 Jul 2017
In reply to Jack B:

The one on my Hudl is pretty good, too.

Just keep it away from metal objects (just like you would for a compass).

Doppler-velocity based bearing is also pretty accurate; much better than delta position values.
pasbury on 17 Jul 2017
In reply to FesteringSore:

Why would you want to put a layer of technology over something that not only works better without it, but is also very understandable and illustrative of a physical phenomenon?

Seems madness to me.
Andypeak - on 17 Jul 2017
In reply to pasbury:

> Why would you want to put a layer of technology over something that not only works better without it, but is also very understandable and illustrative of a physical phenomenon?

> Seems madness to me.

I forgot my compass over the weekend, only realised once the mist had came in and visibility dropped (school boy error I won't be making again). I resorted to using the compass on the os locate app. I obviously had nothing to compare it to but it worked well enough for basic navigation.

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