On 19 November your 0146 ZT position is LAT 33°48'N, LONG 25°22'E. You observe Polaris bearing 359.8°pgc. At the time of the observation the helmsman noted that he was heading 224°pgc and 222.5°psc. The variation is 2°E. What is the deviation for that heading?
• Polaris as a check star for compass error and its relationship to true north • The relationship among psc (per standard compass), pgc (per gyro compass), variation, and deviation • Using the compass error formula: Compass Error = Deviation + Variation (pay close attention to signs: East vs West)
• What does it mean when Polaris bears almost exactly due north by gyro compass? How does that help you find the gyro error (if any)? • Once you know the true bearing of Polaris and the observed psc and pgc, how can you step-by-step move from true to gyro to standard compass (or vice versa)? • How do you decide whether the deviation is East or West when comparing standard compass heading to true or gyro?
• Confirm what the true bearing of Polaris should be at this latitude and time (is it approximately 000°T, slightly off, or very different?). • Carefully track the sign of variation 2°E using a conversion memory aid (such as "East is least, West is best" or your preferred rule). • Before choosing an answer, compute both gyro error and compass error, then isolate deviation from the relationship: Compass Error = Deviation + Variation, checking your East/West signs at each step.
No comments yet
Be the first to share your thoughts!