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Letters addressed by row and column.
Also known as: Polybius checkerboard, Coordinate cipher square
The cipher grid representing each letter by its row and column numbers.
Represents each letter by the numbers of its row and column in a lettered grid.
Contexts: Mathematics, History
Reduces an alphabet to two digits drawn from a set of five, which is what made it usable for signalling by torches, by knocks and later by radio — the encoding was chosen for the channel rather than for secrecy.
Contexts: Mathematics, History
Underlies the tap code used by prisoners to communicate through walls, a use whose value is that it needs no equipment at all.
Contexts: Mathematics, History
A five by five grid of letters with numbered rows and columns, each letter written as the pair of digits giving its position.