If you don't know where this comes from than I would distrust the 345 value. The H.sie scope marks might require a different value to match. It depends on how many marks per degree it has. Try it with a known distance. Ask your watch officer for a distance to a nearby friendly, and your use the periscope to check the formula.
As a first order approximation this formula should work for long distances. But in close quarters the formula might break down. Again, where it stops being usefull is something to be tested in the game.
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