True north

Finding true north

Be sure your instrument is oriented to true north, which in most places on earth is not magnetic north. The difference between the two is the magnetic declination, and it must be compensated for so that the directional information you send to the database on the Internet is the same direction as all other Seismo Sites. This assures that all sites are oriented similarly, and makes the information exchange useful.

map The map shows the difference in degrees that magnetic north varies from true north. It is rough, but adequate for you to compensate your site. Contact Serena for information on how to get your magnetic declination in the U.S., right down to the minute.
Use this map as follows: Locate your position and note the degrees. If you are west of the zero line true north is east (E) of magnetic north. A magnetic compass in San Francisco must be compensated 17 degrees east of true north, or 360 minus 17 degrees, which is 343 degrees. Conversely, a magnetic compass in Atlanta, Georgia must be compensated 5 degrees west of true north, or 360 plus 5 degrees, which is 5 degrees.

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