Your vessel is proceeding up a channel steering on a pair of range lights that are in line ahead. The chart indicates that the direction of this pair of lights is 249°T, and the variation is 14°E. If the heading of your vessel at the time of the sighting is 226° per standard magnetic compass, what is the correct deviation?
• True, magnetic, and compass relationships (T – V – M – D – C) • How to apply variation (14°E) when converting between true and magnetic • How to find deviation using a known true line (range lights) and your compass heading
• Start from the true direction of the range (249°T). With variation 14°E, decide whether magnetic will be higher or lower than true and calculate it. • Once you have the magnetic heading that lines up with the range, compare it to your compass heading (226°) to find deviation. • Think about the sign: if the compass reads more or less than magnetic, is the deviation East or West?
• Be clear on the T–V–M–D–C relationship (for example, one common memory aid is: "True Virgins Make Dull Companions" going from True → Variation → Magnetic → Deviation → Compass). • Double‑check how East variation is applied in your chosen convention (does it make magnetic bigger or smaller than true in your formula?). • After computing deviation, verify whether it should be labeled East or West by checking if the compass reading is pulled toward East or West from the magnetic value.
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