How to Sight a Compass for True North

Using a map and compass to find your way is a practice called orienteering. On maps the compass rose will point toward the true, or geographic, North Pole. Compasses, however, work using the Earth's magnetic field and only point to the magnetic North Pole, which is currently located above Canada, away from the geographic north. The difference, in degrees, between true north and magnetic north changes as you move across the globe. The difference is called an area's declination. In the United States the declination value can change from 19 degrees west in the upper portion of Maine to 18 degrees east in upper Washington State. From Biloxi, Mississippi, to Memphis, Tennessee, and continuing roughly up the Mississippi River Valley, the declination value is zero degrees, meaning compasses point to true north.

Things You'll Need

  • Compass
  • Topographic map
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Instructions

    • 1

      Find the declination value of your current location to true north. The declination value should be marked on the map near or inside the compass rose, and will be given as degrees either east (E) or west (W). This tells you if magnetic north is eastward or westward of true north and to add degrees to magnetic north accordingly.

    • 2

      Rotate the ring around the outside of the compass so that zero, or N (north), is at the top of the compass. This sets the compass value to zero degrees declination. Turn yourself so that magnetic north is sighted between the marks and the compass points to magnetic north.

    • 3

      Rotate the ring to the appropriate declination degree. The declination value will be given in degrees and minuets. Minuets are units of measurements to denote the space between the degrees. West declinations should be subtracted from the compass value and east declinations should be added. Therefore, a declination of 14 W should create a compass value of 346, while a declination of 15 E will create a compass value of 15.

    • 4
      A compass with magnetic north sighted between the marks.

      Turn to sight magnetic north between the marks on the compass. The arrow at the top of the compass will be pointing to true north.