🔍 Key Concepts

• Compass error = variation + deviation • When range lights are exactly in line, the vessel is on a known charted bearing (true) • Difference between standard magnetic compass readings and charted bearings can indicate deviation issues or local disturbance

💭 Think About

• What does it mean, practically, when two range lights are visually in line? How does that relate to your actual track over the ground? • If the range line has a known true bearing, how could you use that to check whether your existing deviation table is reliable? • Would a local magnetic disturbance affect just one compass, or all magnetic compasses in the same location on the vessel?

✅ Before You Answer

• Confirm how psc (per steering compass) differs from readings on the standard magnetic compass • Think about whether matching a visual range alignment with an unexpected compass bearing points to systematic compass error or a temporary/local magnetic anomaly • Before choosing, decide whether the situation described lets you confirm an existing deviation table, or only suggests you need to re‑check it