Calculating a great distance from a ship (or island) to the shore

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Calculating a great distance from a ship (or island) to the shore


From the point of the shore which is found opposite the ship we cover at length of the shore (perpendicularly) a random distance (e.g. 100 steps) where we place a stick and at its extension we cover e.g. the one tenth of the previous distance (10 steps). Afterwards, we walk (perpendicularly) inland up to the point from where we can aim the ship through our stick. Then (due to the shaping of two similar triangles) the distance of the ship from the shore equals to ten times our distance from the shore.