🔍 Key Concepts

• Difference between variation (Earth’s magnetic field vs true north) and deviation (magnetic influences on the vessel)** • Definition of compass error and how it is related to variation and deviation** • What happens to deviation if the only magnetic field acting on the compass is the Earth’s magnetic field**

💭 Think About

• Ask yourself: If the Earth’s magnetic field is the only influence, is the ship’s compass still being pulled by any onboard magnetic sources? What does that do to deviation? • Think about the formula: Compass Error = Variation + Deviation (using proper algebraic signs). If one of these terms becomes zero, what remains? • Consider whether ‘no deviation’ automatically means ‘no difference’ between compass north and true north, or if there is still another difference to account for.

✅ Before You Answer

• Verify the exact definitions: variation is due to the Earth, deviation is due to the vessel. • Check the relationship: Compass = True + Variation + Deviation (with signs). Rearrange it to see what compass error really is. • Confirm what the condition “no magnetic field other than the Earth’s” implies specifically for deviation, not for variation.