In fact, the only thing that the compass does is point the magnetic north. And it’s not the most accurate thing in the world. The needle of the compass can be diverted by large amounts of iron ore, steel objects, power lines and other compasses (when too close). And in these cases, the needle will indicate a false direction. Thus, it is necessary to assess the quality and features of your compass before each field output. Later we will see how to do this.
A current model simple compass is a circular box (capsule) of transparent material. There is a metal part which we call needle. This piece is balanced on a PIN and have free circular motion in horizontal. As the needle is imantada it points, always, to magnetic north. In compasses, the interior of the capsule is filled with a viscous fluid, designed to reduce the “wobble” of the needle. The compasses to be superimposed to the maps are made of transparent acrylic and resemble the drawing above.
Around the capsule, is a rotary ring graduate named Limbo. At the bottom of the capsule there is a series of parallel lines. The thinner lines serve to align the compass (or capsule) to North-South coordinate grid lines of the map. The two central lines (at the bottom of the capsule) are emphasized (thicker, different color, or a special design, see internetdict.com). The track between these internal lines is called Arrow. The Guide arrow is usually in perfect alignment with the 0 (zero) or “N” from limbo. But some compass models allow the Guide arrow is slightly skewed, to compensate for the magnetic declination.
On the base of the compass, leaving the capsule there is a arrow pointing to far end: this is the line-of-Faith. Limbo, depending on the size of the compass, is a graduate degree or degree of 2:00 pm 2 degrees or even more. The smaller the diameter of the limb, more degrees there will be between each pair of tick marks. So, a very small compass offers less precision, because the graduation will have little sharp divisions. A compass that doesn’t have a rotary limbo likewise have little use in practice. Typically the range of Limbo is in degrees. This scale runs from 0° to 360° (or the brand, in limbo), beginning and ending at the same point, named North-of-limbo. The values read in limbo are called Magnetic Azimuth (not to be confused with “course”, which is something different). Are the magnetic azimuth angular values that start in the direction of magnetic north (pointed to by the needle) and a direction chosen by us. This may be the direction of a mountain peak, a big tree, a house or other benchmark.
You probably already know that the magnetic North Pole is away at several kilometers from the geographic North Pole (true). The angular difference between these two poles is called the magnetic Declinaçã. Always keep in mind: the compass has reference to magnetic north, while the maps refer to the geographic North, and the angular difference between them changes forever. See on your map which the annual difference to be compensated. It varies by about 8 minutes per year (1 degree has 60 minutes) about, but your map will provide that information accurately. To prevent you from having to make many calculations, some Compass now come with a declination compensation. The purpose of this screw is misalign the Guide Arrow in relation to the “N” from the limbus, compensating with a declination and angular misalignment in the opposite direction.
As I said at the beginning, the compass only serves to point out directions. It’s up to you to choose the right direction. And to know the direction to follow, you need to know where you are located. In other words: without a map, a compass will serve only to keep us in a particular direction chosen, serving to guide us far more than that. Most of our maps are in very large scales, being often difficult to locate (on a map) our position. This is where the compass is located.