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

Calculate the total change: 3 years (1991-1988) at 6' per year equals 18' of increase. Since the variation was 3°45'W and is increasing, add 18' to 3°45'. The result is 4°03'W. Updating variation is essential for maintaining accurate navigational plots as described in Bowditch.