The 1944 Bletchley Park Cryptographic Dictionary

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SYSTEM INDICATOR :

Discriminant.

SYSTEMATIC :

(of code-books) Having a systematic arrangement which permits the same book to be used both for encoding and decoding, without being strictly alphabetical.

TABLE :

Short for enciphering (or reciphering) table.

TACK ON :

(of two originally disconnected parts or chains of a menu) To be connected by the steckering of a letter in one part to a letter in the other part at a stop in the run.

TAIL :

Figures or letters added at the end of an enciphered message usually to complete the last group of five.

TAILING :

Habit or practice (almost characteristic of Japanese reciphered codes) of beginning the reciphering of the next message at the point of the subtractor where the reciphering of the last one stopped.

TELEPRINTER ALPHABET :

1. The thirty-two characters (including the 26 letters of the ordinary alphabet, the space, 9, letter-shift, 8, figure-shift, 4, carriage - return, 3, line-feed, 4, and oblique /) used to represent the five- (or seven-)unit signals in which teleprinted, esp. enciphered tele- printed, traffic is passed. (e.g. Tunny and Sturgeon).

2. The thirty-two five- (or seven-)unit signals corresponding to the above, which can be regarded as consisting each of a (positive) start impulse, a negative (stop) impulse, and five impulses between these, each of which is either positive or negative. A negative impulse is conventionally represented by a cross (x) and a positive by a dot (.) and the start and stop impulses ignored, so that each character has five impulses each of which can be either a dot or a cross. Impulses are combined by addition, non-carrying, in the scale of 2 (or subtraction, which in this scale gives the same result), a cross being treated as 1 and a dot as 0.

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