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ANNUAL MAGNETIC CHANGE

ANNUAL MAGNETIC CHANGE. The amount of declination for any area will change slightly every year. This difference is called the annual magnetic change . The older the map, the less accurate the information. We can account for this change by using information found on the map:

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ANNUAL MAGNETIC CHANGE

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  1. ANNUAL MAGNETIC CHANGE The amount of declination for any area will change slightly every year. This difference is called the annual magnetic change. The older the map, the less accurate the information. We can account for this change by using information found on the map: 1. Year when map data was last updated 2. Annual magnetic change 3. Declination when map data was accurate GRID NORTH MAGNETIC NORTH 170 mils Year of Map Data 1980 Ann. Change Decreasing .75 mils 405.01 Gold Star OHP-1

  2. STEPS IN CALCULATING MAGNETIC DECLINATION STEP A: Subtract the year of the map data 1997 from the present year. - 1980 17 STEP B: Multiply the answer from Step A by 17 the annual magnetic change. X .75 mils 12.75 mils STEP C: If the annual change is increasing, add the answer from Step B to the declination 170.00 mils when the map data was accurate. - 12.75 mils If the annual change is decreasing, subtract. 157.25 mils 405.01 Gold Star OHP-2

  3. CALCULATING DECLINATION Problem #1: Problem #2: 180 mils 65 mils Year of Map Data 1988 Ann. Change Increasing 2.5 mils Year of Map Data 1982 Ann. Change Decreasing 1.5 mils OHP-3 405.01 Gold Star

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