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SETTING THE COMPASS
The first thing you need to do with your compass before ever taking it into the field is to set its magnetic declination. If you fail to do this, any readings you get from your compass will be erroneous and you may wind up far from where you want to be-LOST. 
The magnetic declination is printed on the front or backside of your GTM. After finding the declination on the map, you need to transfer that information to your compass. If you are using a Brunton compass, you set the magnetic declination by turning the declination setting screw on the side of the compass until the reading on the graduated circle in the compass lines up with the index pin at the top of the compass at the proper declination. For most other types of compasses you can set the declination by simply rotating the graduated circle on the outside of the compass until it lines up with the indicator marker at the top of the compass at the proper declination. Once you have set the declination on your compass, any reading you obtain from it will be accurate. In Wahsington and NW Oregon, the magnetic declination varies from roughly 18°E to 20°E. So, after setting the declination at 19°, when you line your compass up with 0° it will be pointing to true north but it will appear to be 16° off from the ‘N’ printed on your compass. A word of caution here: be sure that you set your declination in the proper direction (east in the Pacific Northwest). If you set it to 19°W rather than east, you will be off by 38° in all of your measurements, rather than the 19° you would be off if you hadn’t adjusted it at all. To make sure you have set your declination properly, orient your compass so that the north end of the needle is lined up with the 0° mark on the graduated circle. If you are located west of the line of zero declination, then the index pin or marker on your compass should be west of the 0° marker on the graduated circle (and vice-versa if you are east of the line of zero declination). |
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