Question 9 AB01 - Able Seafarer

The Correct Answer is B **Explanation for Option B (Correct):** Compass error is the difference between true north (True Heading) and the direction indicated by the compass (Compass Heading). This total angular difference is caused by two components: 1. **Variation (V):** The angular difference between true north and magnetic north. This is geographically determined. 2. **Deviation (D):** The angular difference between magnetic north and the direction shown by the compass, caused by magnetic interference from the vessel itself (e.g., electronics, steel structure). Therefore, the total **Compass Error (CE)** is the algebraic sum of **Variation (V)** and **Deviation (D)**: $$CE = V + D$$ **Explanation of Incorrect Options:** **A) Compass error is variation plus compass course** This is incorrect. Compass course is a direction of travel, measured in degrees. Adding an angle of direction to an angle of error (variation) does not yield compass error. Compass error relates to the difference between true and compass headings, not the heading value itself. **C) Compass error is the difference between true and magnetic heading** This is incorrect. The difference between true heading and magnetic heading is defined specifically as **Variation**. Compass error is the difference between true heading and *compass* heading. **D) Compass error is equal to deviation minus variation** This is incorrect. Compass error is the *sum* (algebraic) of variation and deviation ($CE = V + D$), not the difference between them. While the signs (East/West) must be handled correctly, the formula is based on addition, not subtraction.