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

Correct Answer: Option C — 4°03'W

Magnetic variation updates require calculating total annual change over time and applying it to the base variation. From 1988 to 1991 is 3 years. At 6' per year, total change is 18'. Adding 18' to 3°45'W yields 4°03'W per Bowditch standards.