Marine binocular rangefinder

Now and then I get a question on the "rangefinder" function on a marine binocular that advertises a ranefinder. A good example of such a binocular is the excellent Steiner Commander V 7x50

First, to clear the air, this is not a laser rangefinder. It is an optical grid rangefinder - a far less efficient or useful rangefinder. An optical grid rangefinder in a binocular uses a grid, visible when you look through the binocular, which you use to bracket the object in question. The catch is that you must know the height of the object in question, then do mathematical calculations to determine the distance. Obviously, this is of limited use in the field and, to be honest, it is a feature that survives in marine binoculars more out of tradition than usefulness, unless you just happen to know the height of a ship you are observing.

You calculate range according to the following equation. It does not matter what units you use (feet, yards, meters, kilometers) as long as you use the same unit of measurement for all variables, including height of the object.

Distance to the target equals actual height (must be known in advance) of the target divided by the reticule height (number of lines the target occupies on the grid) times 1000.