In the chart plotting book, what is the Compass Error?

Compass error refers to the discrepancy between the direction indicated by a magnetic compass and the actual direction of true north. The correct understanding of compass error involves both the variation and deviation. Variation refers to the difference between magnetic north (the direction a magnetic compass points) and true north (the geographic north pole), while deviation is the error introduced by local magnetic influences within the vessel, such as metal structure or electronic equipment.

When these two factors are combined, they provide the total compass error that a navigator must account for when plotting courses or navigating. Therefore, accurately determining compass error is crucial for safe navigation, enabling the captain to make necessary adjustments to maintain a correct course.

In summary, the correct choice encapsulates essential components that define compass error and is central to navigation principles.