🔍 Key Concepts

• Line of position (LOP) formed by two charted objects in range (in line) • Difference between true bearing, magnetic bearing, variation, and deviation • How to compute compass error from charted positions and a standard magnetic compass bearing

💭 Think About

• From the two charted lights, determine the true bearing of the range line using their lat/long on the chart. Then compare this true bearing to what you read on the standard magnetic compass. • Ask yourself: does a standard magnetic compass already include deviation, or are you supposed to apply deviation to it? How is variation involved when comparing chart bearings and compass bearings? • Once you find the total compass error, decide which part of that error (variation vs deviation) is fixed for the area and which part depends on heading/bearing and the vessel.

✅ Before You Answer

• Be sure you are using a bearing FROM your vessel TO the lights, and that it matches the charted line direction (don’t accidentally reverse the bearing). • Confirm from your Nautical Almanac or chart what the local variation is in this area before deciding whether any remaining error must be deviation. • Remember that deviation applies only to your vessel’s compass and typically varies with heading; variation is a property of the geographic area and does not depend on your vessel.