how a brunton compass works.
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So they make a variety of compasses, with different features. Fundamentally all compasses work the same. The needle aligns with the earth’s geomagnetic field to indicate North/South.
Some common additional features include
sighting bars to ensure you’re accurately sighting straight to a landmark
Mirrors to ensure that you’re keeping previously passed landmarks behind you while you walk a line. (Ie: walking straight)
Lines to orient with a map
Rulers for working with maps both normal and scaled
There can be many more specialized features added if desired but may not be useful to everyone.
The compass face is reversed, I think, to make it easier to read the direction you are facing.
Suppose you’re looking at a mountain that is north east of you and you want to know what direction it’s in.
If the compass face wasn’t reversed, here’s how you would know that: You’d hold the compass level in front of you and then rotate it until the “N” is beneath the needle. Then you’d see that marking nearest the mountain is “NE”.
But with a Brunton, you don’t have to rotate the compass in your palm. You hold it square to your body. Now you look at the compass and see that the needle is pointing to the letters “NE”. The needle is really pointing towards magnetic north, but by holding it square in front of you while facing directly towards the mountain, you’ve rotated the marked dial under the needle in a way that puts the NE under the needle.
Even better, the sight line part of the compass lets you do that very precisely. You line up the mountain with the sight line and you can now know that the compass body is precisely aligned towards the mountain for a really accurate measurement. If the compass face wasn’t reversed, the sight line part would have to be able to spin — you’d rotate the compass so that the needle is at N, then spin the sight line part around until it is lined up with the mountain, then read the heading the sight line is at. But also be careful not to turn slightly while doing that, or else the needle won’t be aligned with the N mark anymore. With the Brunton, if you turn a bit while doing the measurement, that’s OK, because the markings are rotating with you, and since they’re reversed, it exactly cancels out your movement.
edit to add: It’s also got a little push button which you push when you’re lining up the mountain with the sight line. That button locks the needle in place, so you can now look down at the compass or hold it up or carry it to a place with better light and still get the exactly correct reading.
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