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Shouldn't the title here be "Pratt Semaphore" instead of "Pratt Wig-Wag"? Wigwag signaling is done with one flag and we see two flags here. The Wigwag system is similar to Morse Code in that the most used alphabet letters require the fewest moves of the flags. The Semaphore Code uses two flags, usually divided on the diagonal. See this link for the differences.
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