This white plastic device is part of the Felsenthal Collection of mathematical instruments. One side has twenty-six rows giving permutations of the alphabet. These are labeled on the left with the letters from A to Z. The other side has a thirteen by thirteen grid of rectangles. Many of these rectangles have a two-digit number or two letters in the upper left corner. Toward the center of many rectangles is a term such as “AIRCRAFT” or “ATTACK” or “ROUNDS” that might be used in military communication. The terms are, for the most part, arranged alphabetically going across the top row, then across the second row, and so forth. Not all the rectangles with terms have a two-character corner mark. A slide marked with rectangles, each having a diagonal line, moves across the top of the grid of rectangles. Another slide, also marked with rectangles cut by diagonal lines, moves along the left side.
A label received with the object indicates that is a Borek Communication Code Plotter, made by Felsenthal for the U.S. Army in 1943.
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