Compass Needle Variation

[Humakt]

Now here's a question.
A friend and myself were playing with our compasses and we noticed that they give slightly different readings to a fixed point.
We both took a bearing to the same tree, from the same spot. I had 46 degrees, he had 48 degrees.
Is that kind of variation normal? Neither of us had set for declination.
To me that seems quite a large discrepancy. It'd be fine over a short distance, but anything more than a mile or so and you could be well off.
We were both using Silva compasses - he had a Silva Expedition 15tdcl and I had a Silva Ranger S.
And how do we find out who's compass is off? I must say, I do have a second compass, and I checked mine against that - they both gave the same reading.

[happybonzo]

How near were you to each other when you took the readings? This can sometimes cause a deflection.

[FishyFolk]

When in the army, trired, wet, hungry...I once got out of the vehicle we used, to take a compass reading for a directional antennae we where putting up. Tired I plonked the compass don on the bonnet of the car, and did all my stuff to get a reading on top of that....the antenna was pointed about 90 degrees wrong. Could be the there was some metal around that confused them....

[Martin]

I'd have to agree with the previous replies. There must have been some sort of outside influence acting on the magnetic needle. That the needle points to mag north is a matter of physics. One magnet can't be more or less 'accurate' than another, they just point to magnetic north.

Was your mate wearing a ring? Or maybe he was holding it in the same hand as his wrist watch?

Martin

[Humakt]

Some interesting suggestions.
I think Martin may have something - the friend in question DOES have a ring on his finger. I don't.
This would make sense, since I did have the suspicion that his compass was out and not mine (since I'd checked mine against another compass and both agreed).
The way to see if this is the case would be for me to use both his and mine compass and see if I get the same reading. If so, then the fault must lie with him personally; and a ring on his finger would account for that.
We'll see.
Thanks for the ideas, chaps.

[Ben Casey]

When I was in the Army we always had to put the compass on a flat surface away from buildings and anything metal it made life a bit awkward at times but we didn’t have it in our hands or near enough to our bodies to cause interference.
I ignored it once and took a load of lads in the wrong direction for quite a few miles :(

Needless to say they kicked my backside a bit when we found out LOL

[FishyFolk]

The trouble with the army and compasses ist that there tends to be loads of metal around.... :guns:

[Ben Casey]

We used these LOL

http://farm8.staticflickr.com/7117/7420989822_9865ab3b14.jpg

[Marvell]

Our hand bearing in the boat is a nightmare! Have to get right up the bow where it's all plastic and rubber.

[Old Guard]

When I was in the Army we always had to put the compass on a flat surface away from buildings and anything

Totally agree with this, it's the only way to be sure.

When walking in a group, have a second navigator, who can confirm bearing. If a similar situation happens like yours, then the average of the bearings would be used (46%, 48% = 47%)

[Basha72]

Our hand bearing in the boat is a nightmare! Have to get right up the bow where it's all plastic and rubber.

You need to get one of these

http://www.google.co.uk/search?q=old+sea+ship+compass&hl=en&client=safari&tbo=d&source=lnms&tbm=isch&sa=X&ei=TcXlT5-VJILLsgbksZXZAQ&ved=0CE8Q_AUoAQ&biw=768&bih=928#biv=i|26;d|g12FbPNsp1pTBM:

[spikeuk76]

Another consideration is to check that the damping fluid is still in the Silva if it applies to that particular model. The slight variation in a non sighting compass is no great problem, in normal conditions your compass is pointing you in the direction and then you map to ground to get a more precise indication of travel. Obviously at night, in the jungle, desert or arctic (white out) you rely heavily on the compass needle and others check nav due to lack of points of reference. Also, what everyone else has said!