A Fix can also be obtained by combining a compass bearing and a distance of the same lighthouse.

You can determine the distance knowing the height and the vertical sextant angle of the lighthouse.

Let’s assume you sail near the coast and, looking on your nautical chart, you spot the lighthouse A.

Among the characteristics of the lighthouse, you read that it has a charted height of 103 meters or 338 feet.

This is the height above mean high water spring tide. After calculating the height of tide at that time, the corrected height of the lighthouse is 105 meters or 345 feet.

Use the sextant and measure the vertical angle of the lighthouse.

Let’s assume, after applying the index error, that the vertical angle is 2 degrees and 30 minutes.

Knowing the corrected height and the corrected vertical sextant angle of the lighthouse, calculate the distance, using the formula:

D is equal to h times 0.565, divided by v, where D is the Distance in nautical miles, h is the Height of the Lighthouse in feet, and v is the Vertical sextant angle in minutes.

In our case, 345 feet times 0.565 divided by 150 equals 1.3 nautical miles.