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Al cruzar la oposición Punta Alcázar - Isla Tarifa, tomamos Da de Punta Alcázar = 173º. ¿Cuál es la corrección total?While crossing the opposition line of Punta Alcázar and Isla de Tarifa lighthouses, you take a compass bearing of Punta Alcázar Da = 173º. What is the total compass error?
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Correct answer: c) 8º NW
Why it is correct
On the opposition line between Isla de Tarifa lighthouse (36º 00.0′ N, 005º 36.6′ W) and Punta Alcázar lighthouse (35º 50.9′ N, 005º 33.4′ W), the charted true bearing towards Punta Alcázar is Dv = 165º. Therefore total compass error is Ct = Dv − Da = 165º − 173º = −8º (8º NW).
Why the others are not
- a) Reverses the sign of Dv − Da (giving NE instead of NW) or misreads the opposition bearing on the chart.
- b) Reverses the sign of Dv − Da (giving NE instead of NW) or misreads the opposition bearing on the chart.
- d) Reverses the sign of Dv − Da (giving NE instead of NW) or misreads the opposition bearing on the chart.
How to work it out in the exam
- Measure on the chart the true bearing from Isla de Tarifa towards Punta Alcázar: Dv = 165º.
- Subtract the compass bearing: Ct = 165º − 173º = −8º (8º NW).
Where this question comes from
- Junta de Andalucía · 2021 · 1ª convocatoria · PY Módulo de navegación · question 12 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.