You know what it takes to program your Global Positioning System (GPS) unit, but can you find your way with a compass? Follow this easy lesson for navigating anywhere.
**Compass Anatomy **
The face of a compass shows an azimuth ring divided into 360 degrees. The ring surrounds a liquid-filled capsule with a floating needle pivoting at its center (Fig. 1). The “card” underneath the floating needle may show cardinal points (north, south, east, west) and a “shadow” or orienting arrow that rotates with the ring to set for declination. Rectangular base plates are common now, with a directional arrow that helps you point to and follow bearings.
Find the Right Bearing
To read a compass, hold it level at waist height and away from metal. Bearings are best taken using prominent landmarks far away such as a mountain or a stand of trees. If the compass has a base plate, align the directional arrow with the landmark or intended route, then turn the ring so the floating needle points to 360/0. The degree reading on the ring at the directional arrow is now your bearing (Fig. 2). No base plate on your compass? When facing your direction of travel, with the needle at north, the bearing is the number farthest from you on the ring.
To turn back the way you came, reverse the bearing. For instance, with a travel bearing of 42 degrees, reverse direction on a bearing of 42 plus 180 degrees, or 222; point the base-plate arrow in the direction you want to go and turn the ring until 222 is the number at the arrow (the floating needle should point at 360/0). If your first bearing is 180 or above, subtract 180 to reverse. Heading out at 276, you return at 276 minus 180, or 96 degrees.
Navigation with a Map
Magnetic north and “true” longitudinal north aren’t a perfect fit. To correct for this, good maps contain information about setting “declination” on your compass-the angle of difference between magnetic and true north. Declinations vary depending upon what part of the country you’re in.
Before navigating, first set your compass for proper declination. Turn the azimuth to the correct declination bearing number for your map’s area; on United States Geological Service (USGS) maps this will be labeled “MN,” for “magnetic north.” Then line up the floating needle with the shadow needle by turning your body. Base all further calculations on this declination.
Next, find the bearing of your destination with the compass on the map. Draw a straight pencil line through your location and destination to the map border. Center the compass where the line meets the border, aligning the N-S positions on the compass with the vertical map border. Read the bearing of the pencil line, as if you were facing that direction. This is the degree reading for your direction of travel. As you move, keep the floating arrow aligned with the shadow arrow and follow the bearing.
You can change direction, or relocate yourself if you get off track, by taking bearings off landmarks, drawing pencil lines along those bearings and seeing where they cross (Fig. 3). Your position is the spot where the bearing lines intersect.