🔍 Key Concepts

• Gyrocompass error as the difference between indicated gyro heading and a true direction reference • How magnetic variation and deviation affect comparisons between gyro and magnetic compasses • Using a celestial body's true azimuth as a precise reference for true north

💭 Think About

• Ask yourself: Which option uses a reference that is directly tied to true north rather than to magnetic north or to DR (dead reckoning) assumptions? • Consider which method depends the least on estimated factors such as current, leeway, or steering errors. • Think about how navigators use a sextant and sight reduction to get a very accurate true bearing of a star, sun, or planet—how could that help you check the gyrocompass?

✅ Before You Answer

• For each choice, decide whether the reference used is true, magnetic, or estimated. • Check which method would give you a single, clear numerical error (e.g., "gyro is X° high/low") at a specific moment. • Verify which option matches standard practice taught in terrestrial and celestial navigation for checking gyro error underway.