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How Much Compass Variation Should You Apply

The chart indicates the variation was 3° 45' W in 1988, and the annual change is decreasing 6'. If you use the chart in 1991, how much variation should you apply?

Given:

           Compass variation = 3° 45' W in 1988
                Annual change = 6'

What is asked?
     
            Compass variation

Solution:

              Step 1. Get the year difference. And then multiply the difference by the annual change.                
                              
                          1991
                        - 1988
                               3 
                             ×6'
                              18'


              Step 2. Subtract 18' to 3° 45' because the annual change is decreasing.   

                         3° 45’ W
                      -      18'      
                         3° 27' W is the variation to apply.


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