A Silva Ranger compass is an accurate device used to shoot a directional azimuth. In North America, compasses do not point to the North Pole; they actually point to an area in the Canadian arctic. This means north on a compass and north on a map are rarely the same. A Silva Ranger compass has many features to help you navigate. The compass has a protractor to help obtain bearings from a map and a clinometer to help determine how steep a grade is.
1. Find the difference between grid and magnetic north (G-M angle), using the legend on your topographical map. Most legends are typically found near the bottom of a map. This angular difference is known as declination and is expressed in degrees.
2. Unfold the compass cover so that you will be able to view your target through the site post. The cover should be open approximately 50 to 70 degrees above the base plate. The underside of the cover of the Silva Ranger compass has a mirror and a sighting line on it and the top of the cover has a notched sight post. These will be used together to shoot your azimuth.
3. Bring the compass up to your cheek and look through the sight post with one eye to find your target direction. While keeping the compass level, look down to view the compass in the mirror. While looking in the mirror, rotate the orienting needle to align with the red north needle.
4. Open your compass up and read the bearing number located below the index pointer line. This number is the direction measured in degrees which you just shot with your compass.
5. Adjust the bearing number for declination using the G-M angle from your map. If your magnetic north line is left of the grid north line, you will add the declination amount to your compass bearing number. If the magnetic north line is to the right, you will subtract the declination amount from your compass bearing. This will ensure that you shoot a correct azimuth reading with your Silva Ranger compass.
Items you will need
- Silva Ranger compass
- Topographical map
- The mnemonic LARS is useful to help you to remember "Left, Add, Right, Subtract" to add or subtract the G-M number to your angle.
- Make sure to keep the compass level as this will affect the floating needle of your compass.
- Keep any metal away from your compass, as this will affect your bearing and give you a false reading.
- compass image by Hubert from Fotolia.com