Nope. The needle aligns itself with the local magnetic field, so depending on where you are in the world depends on where it points, sometimes towards magnetic north, sometimes nowhere near it.
Compass
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Nope. The needle aligns itself with the local magnetic field, so depending on where you are in the world depends on where it points, sometimes towards magnetic north, sometimes nowhere near it.
But there is magnetic deviation as well magnetic variation, so unless you know the magnetic deviation you cannot use the compass accurately, "Magnetic north" is possibly the North point of the magnetic field you are stood in at the time...hence it is pointing "Magnetic North" not necessarily global magnetic north...
But there is magnetic deviation as well magnetic variation, so unless you know the magnetic deviation you cannot use the compass accurately, "Magnetic north" is possibly the North point of the magnetic field you are stood in at the time...hence it is pointing "Magnetic North" not necessarily global magnetic north...
Slight confusion over terminology on my part
This conversation will have served to either clarify or confuse the situation for others
Cheers,
Stuart.
This conversation will have served to either clarify or confuse the situation for others
Cheers,
Stuart.
More than likely...
Definitely...
I have a couple of "Stanley of London" prismatic in the arsenal as well as a few Silva types.
Interesting, I thought the needle always pointed Magnetic north, and the bezel was what made it accurate, the bezels are mass produced by the same makers so maybe the degrees are inaccurate as well
OK then, the bezel on a compass marked with 6400 mils is accurate to 25 mils.
The bezel on a compass marked with 360 degrees is accurate to 1 degree.
So which one is more accurate?
Even then it isn't brilliant, but as also mentioned it is very accurate for Artillery fire...1mil being 1 metre at 1Kilometre, so fine adjustments on the traversing and elevation gear on an artillery piece can be called in mills rather than 1/17.8th of a degree...
Silva expedition 4 still strong and true after 15 years plus you have the romer scales on the base plate
Interesting, I thought the needle always pointed Magnetic north, and the bezel was what made it accurate, the bezels are mass produced by the same makers so maybe the degrees are inaccurate as well
Some compasses (my Silva for example) have an adjustment screw so that you can align the needle to point to true north. But you have to reset it if you move to an area with a different variation.
So you can deviate the magnetic field to swing your needle to true North... or you can change the needle to take into account of the Magnetic variation, or both? So how does it actually work on altering the magnetic field of the needle?
There's an induction dampening field inside the bezel. IIRC, when you turn the variation adjustment screww, it moves said field slightly so that the needle swings correspondingly. I'll have a look at the compass a bit later to verify and try to get back here.
The most common adjustment system for magnetic variation is that the compass capsule has a mechanism which allows the capsule to rotate independently of the baseplate and bezel, so that after adjustment the needle points to magnetic north, but the baseplate and bezel align with grid/true north.
Alan.
Alan.
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They're actually on the small instruction sheet that comes with the compass. But my compass (and said instruction sheet) are out in the truck and at the moment I'm watching the Saints vs Seahawks in the second level playoffs leading to the Superbowl.
I have the Silva exped 4 and the Suunto M3. The only thing I've read that puts the Suunto ahead of the Silva is that the bezel is a bit easier to use with gloves. I use the Silva.
The Recta DP420 is the same as the Suunto M3, sometimes it's cheaper.
The Recta DP420 is the same as the Suunto M3, sometimes it's cheaper.
I don't know what model my Silva is but it's a good un, has the 1:50,000 and 1:25,000 grid measuring scale, handy for the old micro nav requirements so dearly loved of us whiteout wanderers, handy for quick accurate map references too.
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