Actually, a smaller wallet sized Fresnel does a pretty good job. But, you’re right, the teeny lens on a SAK or a Compass is not easy to start a fire with.
FYI- it’s also quite difficult with a flint and steel*, even one of those modern flints (although if it has the bar of magnesium, whihc most dudes don’t know about to use, it’s farily easy). The “bow” method requires a lot of sweat and time.
The compasses that have mirrors generally have the mirror arrainged so that it can be used to align the needle at the same time a landmark is being sighted. The mirror also has a line on it that serves as the second sight. (the first usually being a V-notch on the lid) Landmark sightings are done with the lid partially open.
You shouldnt need to adjust for declination when triangulating your position by bearings, should you? You are only getting bearings, not absolute directions.
Absolutely you need to adjust for declination. Imagine a bearing line as radiating from the landmark. You are somewhere on that line. A second bearing radiates from a second landmark. Where the lines cross is where you are. If you don’t adjust these bearings for declination, then these radials don’t extend to your current position.
You’re right, I overlooked the fact that you wouldn’t know how to translate a 35 degree bearing to a 35 degree line on the map, without knowing where 0 was.
Military maps still have them. In a corner somewhere will be a declination diagram saying something like “83 mils, 1.5 per year increasing” which was the best guess of the declination’s movement when the map was printed. I remember one map where the adjustment rate was zero, implying the magnetic pole was either stationary or moving straight to (or away from) the map location.
Just don’t lose the teeny screwdriver that comes with the compass. It’s likely a flat piece of metal tied to the string.
It’s not quite that simple. While the Earth’s field is approximately dipolar, there are other multipole terms as well that can affect local measurements. Most of the variation in any given location is going to be due to those higher-order multipoles, which can in turn depend on things like the mineral content of that location. I wouldn’t be surprised, either, if there were some measurable coupling with the Sun’s 22-year cycle in some locations, too.
Speaking of using compasses to shoot the azimuth, I remember reading an old Disney comic book when I was a babychild where Donald and his nephews were stuck in a boat (?) somewhere with a map and no compass.
Donald used his arms to sight along at a star to find their position… and now that I think of it, that does sound a bit like a primitive sextant, correct? If so, would this actually have worked, with appropriate margin of error, to get our feathered friends out of their state of lost-ness – or was that all made up out of whole cloth by Disney? 