Definition
Measure the vertical angle subtended by an object of known charted height, then compute range. For small angles the range in nautical miles is approximately the height in metres divided by 1.854 times the angle in minutes of arc. Charted light heights are given above MHWS on British charts, so at other states of tide the true height is greater and the raw result is conservative unless corrected. The method is accurate to a few percent inside about three miles.
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