Boussole / Compass
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écrit par Wladimir T.

chef de course et instructeur au Club Alpin Suisse

Le 22 mars 2013

La boussole

La boussole permet de s’orienter dans le plan horizontal. La combinaison carte/boussole permet de déterminer une direction à suivre ou bien l’endroit où l’on se trouve

Elle comporte une aiguille aimantée qui indique le nord, un cadran divisé en 360 degrés ou 400 grades, une ligne de visée et un miroir permettant de voir en même temps la ligne de visée et l’aiguille aimantée.

Dans les Alpes, le nord magnétique fait un angle d’environ 3 degrés vers l’ouest avec le nord géographique.

Pour déterminer le nord géographique, tourner le cadran gradué de façon que le N, l’index nord, soit sur la ligne de visée. Tourner l’ensemble de la boussole en la maintenant horizontale jusqu’à ce que l’aiguille aimantée se place sur la graduation 357 d’un cadran divisé en 360 degrés. La ligne de visée indique alors le nord géographique.

Faire toujours attention à ce que la boussole soit maintenue bien horizontale.
Qu’elle soit tenue à bout de bras ou posée sur la carte, la partie ou se trouve le cadran (et l’attache du cordon) doit être orientée vers l’endroit où se trouve l’observateur.

Le site de la marque Recta donne des informations utiles sur Utilisation de la boussole.

Plus d’infos sur l’utilisation de la boussole.

The compass

The compass allows you to orient yourself horizontally. The map/compass combination can be used to determine a direction to follow or a location.

It has a magnetised needle that indicates north, a dial divided into 360 degrees or 400 grades, a line of sight and a mirror so that the line of sight and the magnetised needle can be seen at the same time.

In the Alps, magnetic north makes an angle of around 3 degrees west with true north.

To determine true north, turn the graduated dial so that the N, the north index, is on the line of sight. Turn the entire compass, keeping it horizontal, until the magnetised needle is positioned on scale 357 of a dial divided into 360 degrees. The line of sight then indicates true north.

Always ensure that the compass is kept horizontal.
Whether it is held at arm’s length or placed on the map, the dial part (and the cord attachment) must be pointing towards the observer’s position.

The Recta website provides useful information on using a compass.

Find out more about using the compass.

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