Degrees of variation (from North)

[Pattree]

Has anyone compared a phone or sat-nav bearing with a reliable compass?

I’ve just bought a cheap compass from Blacks in Keswick.
I’ve just compared it with my iPhone compass and I’m getting a four degree difference!
It may be strange but I’ll trust the magnet before I’d trust the phone. When I get home I’ll do a proper test.

(No, my phone is not set for True North.)

 

[Navaja]

I've just tried with an ancient Silva 7NL I've had since the 80's (reliable I don't know!) and I'd agree at four degrees difference to my phone.

 

[TLM]

They might be "set" to point to different norths, GPS to true and compass to magnetic. When using a map one has to map north to play with.

 

[Broch]

Magnetic declination is almost zero in the UK at the moment - around 0.4 degrees where I am.

One thing to watch out for with phones is that you don't have a magnetic clip cover for your phone. For me to get mine to give any reasonable accuracy I have to switch the phone off (as in shut it down), take it out of it's cover, then re-boot the phone. It can be as much as 90 degrees out if left in its case and it doesn't correct unless rebooted.

 

[nigelp]

I used 3 different models of Silva Compass, compass app on iPhone and also the compass within the OS Locate app.

Phone compass
Indoors the difference was 19°
Outdoors it was 3/4°

The phone compass was more accurate after it had been outside and I wonder if it will recalibrate and the difference will be less once the phone has been outside and on for a few minutes?

Show your workings….
The three Silva compasses and the OS locate one within the app were all pretty much the same. I think the OS locate compass must make some corrections because it knows where it is?

Red line is drawn from the phone compass outside at ‘north’ and the black lines are all compasses.

I teach navigation for a living and for most practical purposes within a group of people, outdoors in the real world, on a good day and all wearing reading glasses the bearing as a ‘number’ will vary by a few degrees! It is also much more about how the person uses the compass, various techniques to keep a straight line across terrain, low visibility strategies, attack points, aiming off etc. Than the bearing as an absolute number. Compass ‘bearings’ are just one tool within a toolbox of navigation techniques.

 

[nigelp]

Has anyone compared a phone or sat-nav bearing with a reliable compass?

I’ve just bought a cheap compass from Blacks in Keswick.
I’ve just compared it with my iPhone compass and I’m getting a four degree difference!
It may be strange but I’ll trust the magnet before I’d trust the phone. When I get home I’ll do a proper test.

(No, my phone is not set for True North.)

Cheap compasses do work but the needle tends to stick when not absolutely horizontal and can be slow to swing to north. Fine for orientation of the map to north but frustrating when trying to use for more open country bearings.

 

[nigelp]

I've just tried with an ancient Silva 7NL I've had since the 80's (reliable I don't know!) and I'd agree at four degrees difference to my phone.

Compasses tend to work or not work! When they error they usually go wrong by 180°. I have very old compasses and they work fine but the liquid inside the housing can get a bit syrupy.

 

[TLM]

Magnetic declination is almost zero in the UK at the moment

From BGS "Over the UK, declination varies by about 5 degrees from the south-east to the north-west."

Apparently at Greenwich it is very close to 0 at the moment.

 

[nigelp]

From BGS "Over the UK, declination varies by about 5 degrees from the south-east to the north-west."

Apparently at Greenwich it is very close to 0 at the moment.

That’s because the UK geographically extends far north beyond the mainland ‘island’.

https://www.ordnancesurvey.co.uk/blog/magnetic-north-continues-its-march-to-the-east

https://www.ordnancesurvey.co.uk/blog/magnetic-true-grid-north-align-over-great-britain

You can shuffle the compass housing around and change the bearing displayed by nearly 2°.

 

[TLM]

Our declination varies from about 6 to 14 degrees, some compasses can compensate even for larger values. It sometimes gets a bit tricky between the 3 values.

 

[Navaja]

Cheap compasses do work but the needle tends to stick when not absolutely horizontal and can be slow to swing to north. Fine for orientation of the map to north but frustrating when trying to use for more open country bearings.

It doesn't stick, moves OK & works fine....
....but it is a little yellow & a bit like a "snow storm" if shaken because of the rust like debris.

I think I shall write a strongly worded letter to Silva, I expect better seeing as I've only used it for around 40 years.

 

[TLM]

But then again 1 degree difference in bearing makes for an error of about 16 m at 1000 m distance so in most cases a few degrees can be forgotten, especially if there are clear way points to recalibrate your position and bearing.

 

[nigelp]

But then again 1 degree difference in bearing makes for an error of about 16 m at 1000 m distance so in most cases a few degrees can be forgotten, especially if there are clear way points to recalibrate your position and bearing.

That’s where strategy and technique come in. The error at 1000m is double the 16/17m because you can be either side of the bearing line, but we are digressing from phone compasses.

@Pattree OP was about the phone compass so when I go out shortly I am going to have another go with the phone when it has recalibrated to outdoors.

 

[Broch]

But then again 1 degree difference in bearing makes for an error of about 16 m at 1000 m distance so in most cases a few degrees can be forgotten, especially if there are clear way points to recalibrate your position and bearing.

In the fog, on top of the Glyders, 16m error can mean a sheer drop of 50m

 

[TLM]

In the fog, on top of the Glyders, 16m error can mean a sheer drop of 50m

True but if you are doing orientation in thick fog with compass in that kind terrain and find yourself falling that is just winning the Darwin Award.

I have been in fairly thick fogs and so far I have been able to see at least say 10 m ahead, if you are doing it during the night you kind of deserve the drop.

 

[Broch]

Nah, the Welsh mountains take on a magical, mystical, atmosphere in mist and fog where shapes loom out at you from nowhere only to turn into a rock formation or a deep peat bank. And, the truth is that the weather can turn in minutes so, even if you started out in bright sunshine, as the air cools anything can happen.

However, I agree, not for the beginner or anyone not up to scratch on their navigation skills - I was merely pointing out that the distance of 16m is not necessarily trivial.

 

[TLM]

I was merely pointing out that the distance of 16m is not necessarily trivial.

In all my years of walking here and there I have maybe half a dozen case of having to follow a compass course for one click or more without a way point. It has always been in thick forest.

My experience on mountainous areas is very limited, skiing in open fells and flying over them in gliders and of course walking in Lapland.

 

[Van-Wild]

I never use my phone for bearing navigation. I always carry a compass, map for primary navigation. For back up I have a Garmin 401 GPS, and then I have the OS app on my phone.

 

[Pattree]

I’d be interested as to whether a GPS such as Garmin suffers the same variation as a phone. Most phones use a magnetometer and are supposed to point magnetic North. I can set my iPhone to true North but I don’t know how or whether the geographical variations are built into the app. I don’t use the true north option.

 

[Ystranc]

One thing to keep in mind is the date that the digital data was licensed for the phone company to use it. Digital data is often several years out of date and this may account for some discrepancies