Definition
Measure the angle subtended between the light or summit and the waterline or base, then compute distance from distance in nautical miles equals 1.854 times height in metres divided by the angle in minutes of arc. Charted elevations are given above MHWS on British charts, so at low water the true height is greater and the computed distance slightly short, which errs safely. Traditional tables such as Norie's give the same result directly. Practical range is roughly 0.5 to 5 nautical miles.
Want to apply this on the water?
Ask Saily out loud for an example, a scenario or a simpler explanation.
Talk to Saily